Biodiversity of Dojran Lake - Europe House

14 Jun

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Biodiversity of Dojran Lake

Biodiversity of Dojran Lake

  1. Geographical and natural features of Lake Dojran (Doiran)

Lake Dojran is the smallest of the three tectonic lakes in Macedonia. At normal water level, it spans over an area of ​​43 square kilometres, with an average depth of approximately 6.7 meters and a maximum depth of 10 meters. Its natural richness is further enhanced by the water it receives from several smaller rivers and sub-lacustrine springs, i.e. springs below the lake’s surface, in addition to atmospheric precipitation. The river Doirani, the lake’s only outflow, starts from the village of Doiran in Greece and ends as a tributary of the Vardar River near the village of Axiochori, Greece.

Lake Dojran is located on the border between the Republic of Greece and the Republic of North Macedonia. It lies at an altitude of 148 metres in the lowest part of the topographic depression, which is bounded by Mount Belasica from the north, Mount Krusha from the east and Mount Machek from the west. At the same time, Lake Dojran is the lowest natural lake in Macedonia. About 64% of the lake is in Macedonian and 36% in Greek territory. The lake has an ellipsoidal or almost round shape. In the vernacular, the lake is also known as Dojranski Gjol.

Due to the natural amenities, hydrological, hydrobiological, geomorphological, regional and other scientific values, and especially the values ​​of the living world in the lake, by the decision of the Assembly of the Republic of Macedonia on 12 April 2011, a law was passed by which Lake Dojran and its coastline were declared for a monument of nature. According to the law, the competent authority for managing this protected area is the Municipality of Dojran. On the Greek side, Lake Dojran is part of the Kerkini National Park.

Monument of nature – a protected area managed mainly for the preservation of specific natural features; an area that includes one or more specific natural or natural cultural features with a special or unique value due to their rarity, representativeness or aesthetic and cultural distinctive features.

Types of lakes

According to the shape and the way they were created, there are several types of lakes of different sizes and depths.

What is a lake?

A lake is a large indentation on the Earth’s surface filled with water. The lake is divided into three parts: the lake basin or the depression where the lake water is located; the lake surface called the lake mirror; and the lake shore. The part of the lake where the water and land meet is called the lake line. Lakes, unlike ponds and other smaller bodies of water, do not dry up and are permanent throughout the year. In natural lakes, the water surface is divided into two parts. The first part is illuminated because the sun’s rays penetrate it, and the lower part, i.e. the bottom of the lake, is dark because the light does not reach it. Winds can move the water in the lake, creating lake waves. The shores of the lake can be steep and rocky, low and sandy in the form of beaches, muddy, or overgrown with reeds, bushes and other types of trees.

How should we protect Lake Dojran?

Lakes are significant for plenty of species and a unique home without which many animals would die out; however, they are subject to constant pollution and destruction by humans and are strongly influenced by a changing climate. If we lose the lakes, we cannot regain them, so keeping and protecting them is essential. Here’s what we need to do:

  1. Formation of Lake Dojran

Due to its age, Lake Dojran hides many secrets about its long geological, biological, and human history. Many turbulent periods of nature and history have been recorded and have an everlasting effect not only on the surface but also on the bottom of the lake.

The main characteristics of tectonic lakes, such as Lake Dojran, are their age and relative stability. The lake’s water surface itself receives a large amount of information that witnesses a multitude of events throughout the years. Actually, old tectonic lakes are like nature’s open-air libraries and archives. Much evidence of past events can be found if the origin, manner of formation, and development of the lake are studied.

There are two sides to the origin of Lake Dojran: one is the scientific one about how nature created the lake, and the second comes from the creativity and tradition of the local population, who sought the explanation of the natural phenomena around them through myths and legends. Through the myths, we can also study the relationship the local population had with the lake over the centuries. This collective knowledge of Dojran teaches us about its importance and the rational use of natural resources. The two most famous legends about the lake’s creation refer to the negative impact of our negligence and failure to pay attention to water and use natural resources wisely.

Geologic features of the lake

Lake Dojran had been created in the Neogene-Quaternary period and has a tectonic-volcanic origin. This means that the basin where the lake is located was formed due to a change in the surface because of the movement of tectonic plates, most likely as a consequence of some kind of volcanic activity. The present Lake Dojran is a remain of the former Peon Lake (also known as Lake Strymon) and belongs to the so-called Pajon group of natural Balkan lakes. It is the relict remains of the former Pleistocene Peon Lake, which covered an area of ​​about 127 km2. The Pleistocene is an epoch that, on the geological scale, covers the period from 1,808,000 to 11,550 years before the present period. This means that Lake Dojran existed at the time when mammoths, mastodons, hipparionines (prehistoric horses) and various giant reptiles roamed the territory. Based on the modern scientific and expert data on the genesis and development of Lake Dojran, a general conclusion can be drawn that it is a typical eutrophic lake from the Pliocene era, that is, with an age estimated at several million years.

The total length of the coastline is 24 km. This coast has the smallest branching, and a large number of sandy beaches have developed through it, which has crucial potential for the development of tourism. Most of the lake is covered with clayey material, and only the steeper terraces are sandy, which is one reason for the turbidity of the water.

1.First legend:

On the present Lake Dojran site, a wide valley with lush meadows, gardens, and orchards stretched. On a small hill at the end of the valley, there was a large water spring. Next to the valley, a beautiful girl called Dojrana lived. Many boys were in love with Dojrana, as well as a Turkish renowned man-kaymakam. Dojrana could not imagine marrying him. The kaymakam started walking after her. He followed her every step of the way. He did not give her peace. Finding herself in a hopeless position, without falling into his hands, she threw herself into the great spring. The water spring accepted her body. To cover and sanctify him, the water spring began to spill over. It covered the entire valley. In a short time, the valley turned into a lake. The lake and its shores were supposed to remind us of the beauty of the beautiful Dojrana. The lake and the town were named after the beautiful girl Dojrana. In her honour and eternal memory, the lake was named Lake Dojran, and the town – Dojran.

2.Second legend:

In the historical town of Pauline, there was a very beautiful girl named Dojrana. She was tall, slender and had black eyes. Her beauty became known throughout the local area. Dojrana and her friends came every evening to the fountain, which was placed in the spacious valley at the end of the town.

One evening, when Dojrana went to get water with her friends, the handsome Labin came to the fountain. While Dojrana and Labin were talking gently and lovingly, Dojrana’s friends filled the clay water and metal pots with water and went home. Dojrana and Labin were left alone. They stayed for a long time. When they realised that her friends had left and left her alone, she got very confused, so she quickly filled her pots with water and hurried to catch up with her friends. It was dark, and she was afraid to go home alone. In her rush to catch up with her friends, she forgot to turn off the tap. The water from the tap was flowing all night long, so the next day, the people were flabbergasted that the whole valley was flooded, and instead of a beautiful grassy field, a lake was formed. When the villagers and farmers understood that Dojrana had forgotten to turn off the tap and had left the water flowing over the night, they decided to name Dojran this new Lake after her, and the town Polin was renamed Dojran.

  1. Lake Dojran and the local community

Lakes and lake shores have always been locations where people established their first settlements and habitats. The lake was the primary resource of drinking water, irrigation water, food and construction materials. The old tectonic lakes, such as Lake Dojran, have always been the centre of local culture and civilisation. Throughout the turbulent historical period, peoples, cultures, rulers and languages ​​changed on the Dojran coast – and from all this, only a few archaeological artefacts, many tales, parts of the tradition and, of course, the lake, silently witnessing the past of the entire region, remain today.

The oldest recorded evidence points to life by the lake in the 5th century B.C. More significant development of the settlement was noted in the Roman period, and when Dojran was under Byzantium, it was given the name Polin, meaning “town”. When the Slavs arrived, the settlement received the Slavic name Poljanin. The surroundings of today’s Old Dojran began to develop after the arrival of the Ottoman Empire and began to function as a small market town. After the destructions in the First World War, when Dojran found itself on the borderlines of the three warring parties, the town was destroyed, and the population retreated and formed the new community of New Dojran.

Presently, three settlements bear the name Dojran: Old Dojran and New Dojran on the Macedonian side and the village of Doirani on the Greek side.

The surroundings of the lake are inhabited by the local communities of 13 villages: Durutli, Gjopcheli, Kurtamzali, Nikolikj, Nov Dojran, Organdjali, Sretenovo, Sevendekli, Star Dojran, Furka, Crnichani, Chaushli and Djumabos.

From the collective knowledge and memory of the local population, we can learn a lot about the lake’s ecology and how it has changed over the years. The Slavic name for the town of Poljanin may refer to the fact that throughout history, the lake had periods of drought and withdrawal of the lake water, which gave the lake the appearance of a flooded meadow or field. The local name for the lake is Dojranski Gjol. Gjol is an archaic term of Turkish origin that means a swampy area. This also does not lead to the possible conclusion that the nature of the lake is closely related to the local water cycles that the local population has in their collective memory of the lake.

Fishing with “mandras”

Fishing is an essential economic branch for the population living in the vicinity of Lake Dojran. It is characterised by the traditional way of catching fish with the help of waterfowls and fences made of reeds called “mandras,” in which the fish escape from the diving birds. Fishing with mandras is a rare example of humans using wild species (in the case of cormorants) to hunt and catch fish.

The mandras are a direct physical artefact between the present and the lake’s oldest building forms. It is considered that all tectonic lakes in North Macedonia were initially inhabited by so-called stilt-house settlements, where people resided and fed themselves on the water surface itself. The locals built small houses using natural and local materials from wood, reeds, and hay. The houses were placed on tall, wooden poles near the lake shore.

Lake Dojran is one of the few places in the world where fish are caught with the help of birds. This process is a sporadic fishing tradition in the world. Mandra is a water area in the lake near the shore, in which there is a house, and it is surrounded by reeds on three sides. The preparations for fishing in this old traditional way begin in October and last until March. In October, two sides are fenced with reeds, and the side facing Lake Dojran is left open.

When the cormorants arrive in November, they approach the fence in search of food, chasing the fish away. When the fishermen find that there is enough fish, they completely enclose the mandra. They catch the birds in the area called pilikatnik, cut their wings and release them on the fence by the lake to guard the fish and prevent them from leaving the enclosure. Birds with clipped wings are called “labourers”. As time passes, the fence gets narrower and closer to the shore, creating a small area called a box from which the fish are drawn without physically damaging their bodies.

  1. The environmental disaster of Lake Dojran

 

Changing water levels is part of lakes’ natural process. Lakes are ecosystems that are created, exist, and age. That is why it is said that lake ecosystems have three ages: the age of the lake basin—when the lake formed; the age of the water system—when the lake basin filled with water; and, most importantly, the age of the lake as an ecosystem, that is, when life began in it.

Throughout its evolution, Lake Dojran has recorded a continuous decrease in the maximum water level. This decline is very slow (several meters throughout millions of years) and is considered the lake’s natural ageing. However, with the digging of the Gjol Aj drainage channel by the Greek side in 1808, this process has drastically accelerated, and the water level in the past hundred years has been subject to great oscillations and changes.

From 1951 to 1994/95, the lake’s water level oscillated between 148.04 and 142.01 m above sea level, a height difference of 6.03 meters. These fluctuations caused the water volume to vary by 226.4 million cubic meters, which represents as much as 74% of the total lake water volume at the lake’s maximum level.

Between 1984 and 2003, due to uncontrolled discharge of water, excessive evaporation, and long-term drought, the lake recorded a continuous drop in its level with an average annual loss of 5.73 million cubic meters of water. Because of this, Lake Dojran was facing enormous environmental disasters during this period. This is the first example in the country’s history where we face a severe ecological catastrophe that poses the danger of the complete disappearance of an important ecosystem and the loss of the entire lake.

With the project “Rescue for Lake Dojran” of the Government of the Republic of Macedonia in 2003, a hydro system was commissioned through which the lake is supplied with additional amounts of water from the alluvial outcrop in “Gjavachko pole” in the vicinity of Bogdanci. With a utilisation of 90% of its capacity, the system brings about 28 million cubic meters of water annually to Lake Dojran, which, in addition to some other positive aspects, contributed to the return of the lake level to optimal limits.

Although the water level can be controlled, a major ecological disaster has irreversibly destroyed many rare and unknown species and rare natural communities.

Pollution of lakes

All aquatic ecosystems stand for an open surface where various pollutants end up. If the air is polluted, the pollutants fall on the water’s surface and pollute it. If the soil is contaminated with the rains, it is washed away, and the pollution is transferred back into the waters. If, on the other hand, the river that flows into the lake is polluted, the polluting substances also flow in with it. Today, aquatic ecosystems represent some of the most sensitive and polluted ecosystems under constant threat.

Waste

Solid waste greatly harms the living world in ponds and lakes. Its shape and size can physically injure animals. Some of the waste looks like food that animals can swallow and suffocate. With its weight, some waste destroys underwater nests or eggs, and sometimes solid metal or ceramic waste litters the lake bottom.

Water pollution

Very often, due to human irresponsibility, various forms of pollution and poisons enter the ponds and lakes and impair or completely destroy the life in them. Some substances act like poison on fish, frogs and other animals and poison them. Other substances affect the life of insects, leaving fish and frogs without food. There are pollutants that cloud and change the water, causing complete destruction of the lakes.

Warming of water

The long and warm periods cause an increase in temperature in ponds and lakes. The strong sunlight penetrates the entire water surface, bringing light and heat. Although we may enjoy hot showers and baths, we only enjoy them for a short time, and then we feel hot and stuffy. Similarly, rising water temperatures affect living organisms in the lakes.

Drying up of the lakes

As temperatures rise year after year, summers become longer, days longer, and rain less frequent, and the lakes begin to dry up and disappear. Drought causes the water to evaporate from the lakes, reducing the space where animals can live. As the water recedes, all the animals and plants that live near the shoreline are left on dry land and die. Due to their size and depth, the lakes are slightly more resistant to drought, unlike ponds, which can disappear in one summer.

Destruction of the lakes

Humans are not always aware of the value and sensitivity of lakes, so they constantly destroy them with their construction plans. With the desire to expand the areas in which he grows food, man dries up, buries and fills ponds and other small areas with water. The shores of the lakes are essential for the movement of animals, and man who wishes to live or enjoy near the lakes destroys the shores by building houses, embankments, and ports.                                                               

  1. The birds of Lake Dojran

Lake Dojran and its surroundings is an important place for birds. Here, they stay, feed, breed, nest, rest and hibernate. The lake, full of fish and food, is a vital feeding centre for many species of waterfowl. Reeds and riparian vegetation offer ideal conditions for nest formation and hiding from predators. The relatively weak urbanisation of the coast and the surrounding area offer a wilderness that represents a peaceful and safe shelter for birds.

Lake Dojran is especially important for migratory birds. For them, this lake has two roles: as a way station, where they can rest, feed, and take shelter in adverse weather conditions, and as a final destination.

Bird migration is a seasonal flight from nesting sites to wintering sites.

By protecting important bird areas, the conditions in which migratory birds live are improved.

The bird population is especially large during winter when birds from more northern regions find favourable climatic conditions for wintering here. The number of birds in the winter months is regularly monitored, and it can be concluded that in winters with very low temperatures, their number is significantly lower when the lake freezes.

As representatives of the avifauna, the presence of the curly pelican (Pelecanus crispus), little cormorant (Phalacrocorax pygmeus), white-headed duck (Oxyura leucocephala), great cormorant (Phalacrocorax carbo), blue-legged swordsman (Recurvirostra avosetta), little swan (Cygnus columbianus) is significant, marsh harrier (Circus aeruginosus), common pelican (Pelecanus onocrotalus), purple heron (Ardea purpurea), masked shrike (Lanius nubicus).

The curly pelican

The curly pelican is a migratory nesting bird of the pelican family. The pelican is a large, heavy-flying bird. It has “curly” (curled) feathers on the crowns and nape, hence its name. It has a large, strong yellow-orange beak with a large orange throat pouch underneath. The average weight of 11.5 kg makes it the heaviest bird of its kind in the world. They have among the largest wingspans among birds.

Little cormorant

Little cormorant is a large water bird from the cormorant family. The body of the little cormorant has dark feathers with a green tinge. It has a long tail and a thick beak with a distinctive appearance. It is a partially migratory type of species. The little cormorant lives and breeds in colonies in freshwater lakes with a lot of vegetation like Dojran. It builds a nest of grass and twigs on low trees. The little cormorant feeds mainly on fish, often hunting in a group. It is precisely because of this characteristic that this species is traditionally used in Dojran for hunting fish in “mandras”.

Great egret

The heron is a large water bird whose life is associated with water bodies. She can often be found along the shores of ponds and lakes, diving headfirst into the water looking for food. The heron feeds on fish, frogs, and less often on mice. She uses her long yellow beak sharp like a spear to hunt fish. It lives and nests in groups called colonies.

Bee-eater

The bee-eater is a small, migratory bird that can often be found around the shores of ponds and lakes. It is a very colourful bird whose body feathers are red, yellow, green and blue. Instead of a nest, they live in holes they make along the banks. Most often they live in a community, i.e., there are several holes on one shore. It is called a bee-eater because it feeds on insects, mostly bees – but in addition, it also feeds on other insects such as grasshoppers and butterflies.

Birdwatching

Birds are one of the most studied groups of animals because many people consider watching them a hobby. Birdwatching is the process of studying birds and their ecology by observing their lives with an optical aid (binoculars) and listening to their song and sounds. Some species can be determined by physical observation, and some are recognised by their song.

  1. The amphibians and reptiles of Dojran

Lake Dojran, as a water ecosystem with its small and rare habitats and coastal vegetation, represents a “hot spot” for a large number of species of amphibians and reptiles. They inhabit the lake, coastline, riparian vegetation and reed belts in Dojran.

Amphibians are cold-blooded vertebrate animals that spend one phase of their lives in water. They differ physically between their aquatic and terrestrial phases. Unlike reptiles, they lay their eggs in the water. Adults feed by hunting insects and larvae.

Reptiles are cold-blooded, vertebrate animals such as snakes, lizards, and turtles. Most species lay eggs, but only some give birth to live young. Their skin is covered with scales and bony plates that can be located under the skin.

The most common species of amphibians in Dojran

The most common types of reptiles in Dojran

Marsh frog

The marsh frog is an amphibian that lives in both ponds and lakes. It is recognised by its dark green or brown body with a light green line across its head and back. During the day, the marsh frog moves by swimming in the waters; at night, it comes ashore to hunt. It has a large appetite and can feed on different types of food: flies, butterflies, moths, snails and other insects. During the winter, the marsh frog hibernates in the mud by the lake water or in natural holes along the shores.

Crested newt

A crested newt is an amphibian that lives in small bodies of water such as ponds. It looks like a lizard and has a strongly developed tail that moves through the water, making it an excellent and fast swimmer. The crested newt lives constantly underwater, except during the winter when it hibernates on the sandy and muddy shores of the ponds. Due to the colouring of its body, it is tough for us to notice it moving through the murky green waters of the ponds. It feeds on various aquatic insects

Dice snake

The dice snake is a non-venomous snake that lives near rivers, ponds and lakes. It feeds on fish, amphibians, reptiles and insects. Its body is oblong, with grey-green skin and dark spots on its back. The dice snake is an aquatic snake that can swim and dive while hunting and sometimes moves around the shores of ponds and lakes where it waits for its prey. When this snake senses danger, it secretes a foul-smelling substance from the back of its body to defend itself from enemies.

Capturing, hunting, mistreatment and killing amphibians and reptiles within Lake Dojran, the Monument of Nature, is strictly prohibited! 

  1. The living world in and around Lake Dojran

Lake Dojran is a small European oasis of rare and endangered animals. From the deepest depths of the lake, through the lake surface, the coast, the beaches and the shores, all the way to the small lake forests – all of the place blooms with life in various forms, preserved in Dojran throughout the millennia.

Lake Dojran and its surroundings are an ecosystem of significant relevance, being home to almost thousands of species of invertebrates.

The expansion of invertebrates throughout the Dojran region can be divided into three main parts: life in and on the water, life on the coast and life in the surrounding hills and meadows.

Although not aquatic ecosystems, the hilly mountain landscapes, meadows, orchards, fields, and gardens of the Dojran region are directly related to the lake. Many species move daily from terrestrial ecosystems to the lake and vice versa, which means that their presence is an important part of life around the lake.

Life in the water

The common wildlife present in Lake Dojran includes the type of Porifera (sponges) with its three species, including the endemic Dojran sponge Spongilla carteri dojranensis.

The type Mollusca (mollusks) in Lake Dojran is represented by the species belonging to the two classes Gastropoda (snails) represented by 21 species, including the Dojran endemic snail Graecanatolica macedonica and Bivalvia (shells), five species of which the most striking species is Dressena polimorpha.

The subtype Crustacea (crabs) is richly represented in the waters of the lake, and the class Copepoda includes all three orders of freshwater copepods, the endemic Dojran cyclopoid Microcyclops varicans dojranensis.

Life on the coast

The class Oligochaeta (earthworms) is represented by 22 species in Lake Dojran, especially the Dojran endemic species Isochaeta dojranensis.

In the benthic community, these are insects and other invertebrates that live at the bottom of lakes. They are characteristic of spending their lives as aquatic insects during the larval stage and on land during the adult period. Thirty-nine species have been registered from the order of dragonflies (Odonata). Among the representatives of the order of stoneflies (Plekoptera), the species Rhabdiopteryx dojranensis is a Dojran endemic.

The order of butterflies (Lepidoptera) includes a 526 species in the Dojran Basin and the Dojran Basin, which represents a massive concentration of diversity in a specified territory. This high species diversity is due to the different number of small habitats throughout the region.

The great water beetle

The great water beetle is a large aquatic insect from the group of hard wings; we call them this because their wings are hidden by hard shields, which they open when they need to fly. The water beetle is a super insect; it can fly and run on the ground, and also swim and dive. It feeds on small insects, larvae and also on plants that decay in the water. To survive, its larvae attach themselves to the snail’s shell and live there until they grow up.

Fishing spider

The fishing spider is a frequent inhabitant of ponds and lakes. It spends its life half in water and half on land. It cannot swim or dive, but it uses its eight strong legs to glide on the water’s surface, and sometimes, it looks like it is paddling a kayak. It is an excellent hunter and, just like fishermen, sits calmly on the water’s surface and waits for its prey. Sometimes, it stands still on a branch near the shore and prepares itself to hunt, and only when it thinks that the prey will escape, for a short time, can he dive and pull it out of the water.

Crustacean

The crustacean is a nocturnal inhabitant of lakes. During the day, it stays calm and rests in a hole or cracks on the banks, and in the evening, it comes out to move and feed. Its menu includes worms, snails, aquatic insects and sometimes aquatic plants. Still, the crustacean is also an important food for other animals, especially predatory fish. The crustacean can be recognised by its tail covered with small armour-like plates as well as its pincer-shaped front legs. The most essential thing in a crustacean’s life is clean water – it can and wants to live in clean lakes, ponds and rivers only.

Dragonfly

The dragonfly is a large, fast-flying insect that is often found around the shores of ponds and lakes. It is easily recognised by its appearance and strong wings. This insect’s life is divided into two parts: half of it is spent as a larva under the surface of the water, and the other half is spent flying around the lake and marsh reeds. The dragonfly is a strong hunter, grabbing its prey with its legs and eating it while flying.

Mayfly (dayfly)

The mayfly is a tiny flying insect found near the shores of ponds, lakes and rivers. It is easily recognised by the three small thin tails that protrude from the back of the body. The mayfly is most active during the spring and summer days. The mayfly spends most of its life underwater, attached to rocks and water grasses. Then, it emerges from the water’s surface, opens its wings and lives for a very short time, sometimes only one day – hence the name dayfly.

  1. The algae in Lake Dojran

Algae are autotrophic plant-like organisms that feed themselves through the process of photosynthesis. Their body is slightly differentiated and is referred to as a thallus. They can be from very small unicellular, up to large and several meters long. Some of them in the water take on the appearance of underwater plants. Algae are mostly green in colour, and sometimes they can be yellow, brown or red. They can be found in both fresh and salt water. The algae have a vast expansion on Earth. They live in an aquatic environment, which is the most favourable for their development. However, they are also found in humid and occasionally wet places. In addition, they live on rocks and snow, in soil, in some plants and animals, as well as in symbiosis with fungi. Algae are cosmopolitan organisms, i.e. they are widespread everywhere.

In Lake Dojran, in addition to living on the bottom and across the water’s surface, they can also live on the surface of the water, along the shores and beaches, or attached to stones and rocks.

Eutrophication and emergence of aquatic bloom

Eutrophication is a process that takes place in the ecosystem of a water basin (lake) when the amount of chemical substances used in the mineral nutrition of plants (nitrogen, phosphorus) increases, which leads to increased biological productivity. During this so-called “water bloom”, some adapted species of algae develop abundantly and increase their biomass many times. The aquatic bloom is most often due to some type of blue-green algae. The blue-green algae (cyanobacteria) are small, single-celled organisms capable of photosynthesis.

Due to the presence of large amounts of nutrients of biogenic origin, among which phosphorous and nitrogenous compounds dominate, Lake Dojran is distinctly eutrophic with a tendency to hypertrophication. The lake is characterized by the overproduction of phytoplankton and algae whose quantities repeatedly exceed the needs of the organisms that feed on them. On the other hand, the water is deficient in oxygen, which negatively affects the conditions for the development of the living world.

Lake ageing

With the deposition of dead biological material on the bottom as a result of eutrophication and increased sedimentation, the water basin gradually turns into a swamp and then into a terrestrial ecosystem. That is why this process is also known as “lake ageing”.

  1. The fish in Lake Dojran

The fish in Lake Dojran

Lake Dojran represents one of the most important water ecosystems in the country due to its great biological diversity and different types of fish. In terms of the composition of the most abundant fish, Lake Dojran is a cyprinid lake, i.e., a lake in which fish from the carp family and their related species live mostly.

According to their origin, fish in Dojran can be autochthonous or allochthonous. Autochthonous species naturally belong to the area and the ecosystem; they are part of the native biological diversity. Allochthonous species are species that cannot be found naturally in the lake and have been introduced by man. These types of fish ended up in the lake due to stocking, i.e., enrichment of the lake’s fish stock to develop fishing.

Today, the intake of allochthonous fish species is not recommended and is strictly prohibited.

The fish stock of Lake Dojran counts 14 species, of which only one is endemic, while two species were introduced. In the past, the number of fish species that could be found in the lake was 21 species from 7 families. Still, some species, such as black barbel, gudgeon, chub, or golden clipper barb, are very rarely or not at all encountered, while a specimen of stone loach has not been caught for more than 40 years.

Over a century of research has focused on the types of fish in the lake and their lives. However, due to the ecosystem’s complexity, biological secrets are still hidden under the calm lake water of Dojran.

Fish

The fish are aquatic vertebrates with fins and internal gills. They spend their entire lives in the water. The fish had a smooth, torpedo-shaped body composed of three distinct segments: head, body, and hind fin. Depending on the species, some fish have a different number of fins with a variety of shapes across the body parts. Some species of freshwater fish have a body covered with hard scales. In the skin, there are glandular cells that secrete a slimy substance that allows them to move more easily in the water.

The biological diversity of species in an ecosystem is called ichthyofauna. The presence and quantity of fish that are important to fisheries is called the fish stock.

The importance of fish to birds

Lake Dojran is an extremely important destination for resting, staying and breeding migratory and non-migratory waterfowl precisely because of the richness of the fish stock in the lake waters. Fish are the main and most important source of food and energy for many water birds.

The migratory birds travel thousands of kilometres every year and Dojran provides a safe place where they can rest and feed during their long seasonal migrations across seas and continents.

Protecting the food chain

By protecting fish, we protect the natural food chain in the lake ecosystem. The aquatic invertebrates feed on plankton, fish feed on aquatic invertebrates, and birds feed on fish. To preserve the ecosystem, these natural chains and cycles must not be stopped or disturbed.

Feeding and throwing food to fish from the lake shore!

It is prohibited to feed fish human food, especially snacks, oil-fried and salted nuts, or pastries. This food is not intended for fish and may harm their health!

If you wish to do recreational fishing, always pay attention

Illegal fishing reduces fish stocks and local biodiversity.

The most common types of fish in Lake Dojran

Common carp (Cyprinus carpio)

Carp is a type of fish that belongs to the carp family. It lives in slow-flowing or non-flowing waters, which can often be found in the lower reaches of rivers and lakes and also in deeper swamps and ponds. The carp is a large fish with a laterally flattened body covered with large scales. Each scale has a small dark spot on top. There are two pairs of whiskers at the ends of the mouth. The carp is a fish that can be farmed successfully.

Common roach (Rutilus rutilus),

The roach belongs to the carp family. The fish has an oblong, laterally flattened body covered with large scales. Its fins are red, which is why it got its name. In addition to the fins, the iris of the eyes is often red as well. The subspecies Dojran roach (Rutilus rutilus dojranensis Karaman, 1928) is characteristic of Dojran. Fish move through the water in large schools that depend on the size of the ecosystem they inhabit. Although it can be found in greater lake depths, the roach spends most of its life close to the shore.

Common bleak (Alburnus alburnus)

Bleak is a type of river and lake fish from the carp family. It is recognised by its elongated, silvery white body with a pearly sheen. A dark grey thin line runs along the sides of the body from the head to the tail. The bleak moves through the water in large flocks. It spends most of its life in the deeper parts of the lake except during the spawning season when it can be found near the lake shore. This type of fish has high commercial importance.

The predatory fish in the lake

The eel (Anguilla anguilla) – very rare

The eel is a large, elongated fish that inhabits lakes and seas. Its body has a snake-like shape, which is laterally flattened in the back to move through the water. The whole body is covered with scales and, over them, a thick mucous layer. The colour of the skin of the body depends on the substrate of the lake it inhabits. The colour of the eel changes from silvery white to bluish metallic grey during the period when it goes on its famous wedding journey. They are active only at night and rest during the day in the sludge and silt at the bottom.

Perch (Perca fluviatilis)

The perch is a medium-sized fish that lives in lake and swamp water and can be found in shallow and slow-flowing rivers and streams. The body of the fish is covered with small scales, and on the skin, there are distinctive black parallel spots that go around the body. Sometimes, these spots had the shape of the Latin letter “V”. They are distinguished by their strongly developed fins and sharp teeth that are hidden behind a well-developed mouth. During the day, they move through the water in a school; in the evening, the school breaks up, and they spend the night in the lake depths.

Catfish (Silurus glanis)

The catfish is a large freshwater fish that inhabits ponds, lakes, rivers and streams. It has a long strong and smooth body. Unlike other fish, there are no scales on its skin. The catfish is easily recognized by the three pairs of long whiskers that surround its mouth. It feeds on small fish and also on other small animals. The catfish likes to live and spend most of the day hidden in a hole or process on the shores of a lake or pond. It has very small eyes and poor vision, but it uses its highly-developed hearing to navigate through the water.

  1. The flora of Lake Dojran

  2. Lake Dojran and its surroundings represent an important area for the development of rare plant species.

The flora of Dojran, depending on the places where it can be found, can be divided into underwater vegetation (plants that grow in lake water), riparian or coastal vegetation and the vegetation of the surrounding hills and meadows.

The most characteristic plant element of Lake Dojran is the reed zones that identify the lake.

Cane zones

Reed zones are among the most important habitats in Dojran Lake. The dense belts offer shelter and are home to many species of animals. Reeds are a type of perennial herbaceous plant that grows in large clumps called sedges on the shores of lakes and ponds. The reed can grow several meters in height, and completely separate the water from the shore. With its density, reed beds are home to a large number of animals, especially waterfowl that lay their eggs here. The reed is a kind of filter that purifies the water.

Underwater vegetation

Among the submerged plants, the most common are Ceratophyllum demersum, Najas marina, Potamogeton perfoliatus, Myriophyllum spicatum, Vallisneria spiralis, etc. The species Najas minor is restricted to the shallower southern edge of the lake, while Myriophyllum spicatum is present in almost all communities and develops most abundantly at depths of 40 cm, forming huge underwater meadows.

Najas marina and Potamogeton perfoliatus develop almost equally luxuriantly, the difference being that Najas marina penetrates to a depth of 3 meters, while Potamogeton perfoliatus even deeper.

Vegetation in the surrounding meadows

The rare species Centaurea rifidula, Verbascum doiranense, Verbascum burgeffi and Astragalus thracicus doiranensis are described from sites within the Dojran basin or close to it.

Riparian vegetation

Riparian or riparian vegetation represents the area of ​​vegetation that follows the shoreline of streams, rivers, lakes, and wetlands. The healthy riparian vegetation is composed of trees, shrubs and tall grasses that shade the water and stabilize the banks.

The natural, riparian vegetation along the banks is an important habitat for terrestrial and aquatic animals. The trees with their high canopies provide shade and reduce the water temperature, thus providing a good life for fish and aquatic animals. The trees are also home to many species of mammals and birds. The large and deep roots, on the other hand, stabilize the soil and maintain the banks.

Riparian vegetation management and protection improves water quality, prevents erosion and protects species.

The destruction of the riparian vegetation directly increases the temperature in the water, which destroys the fauna and changes the flora. All this leads to a decrease in the amount of oxygen in the water and increases the possibility of the development of invasive species of plants, resistant to higher temperatures.

The coastal, riparian vegetation is one of the most endangered ecosystems across Macedonian rivers and lakes. Due to poor management of forest areas and agricultural practices, a large part of the coastal vegetation is damaged or significantly reduced.

Dojran plane trees

Along the entire western coast of Lake Dojran, one can see individual and groups of plane trees, some very old and some planted in the past decades. However, the most impressive examples are those in the park and the square near the municipal building in Star Dojran. Due to their age and environmental impressiveness, in 1970 the Republic Institute for Protection of Cultural Monuments from that period made a decision by which this community of Platanus orientalis trees was declared a natural monument.

  1. Lake Dojran – a protected natural monument

Lake Dojran is a protected area from the category of Monument of Nature, and its surroundings represent an important part of the national and world natural heritage. Almost every part of the nature of this area enjoys some form of protection or worldwide, scientific and international recognition for its values.

Lake Dojran is a key area for biological diversity. These are areas of international importance for the conservation of biological diversity that are identified through globally standardised criteria based on the needs of site protection for biodiversity conservation and are characterised by a) sensitivity (presence of endangered or critically endangered species) and/or b) irreplaceability (presence of endemic species with limited expansion, gathering places of a large number of individual congregations and/or biogeographically limited communities).

Lake Dojran is a small depot of endemic species. Endemics or endemic species are species that are limited or observed only in a certain geographical space or area. The size of the area occupied by the endemic taxon varies; endemics that are limited to a narrow area are stenoendemites. According to the time of emergence, they can be paleoendemites (old endemics) and neoendemites (newly emerging endemics).

Due to its geographical location, Lake Dojran is a significant area for birds. It is an area that supports significant or representative populations of one or more bird species, determined according to internationally agreed criteria; also known as an important bird and biodiversity area.

The great endemism of plants makes Lake Dojran and its surroundings an important plant area. These are areas that are globally important habitats for plant conservation. They are identified according to pre-set criteria, such as: the presence of world, European or national endangered plant species or the presence of European-threatened habitats.

Lake Dojran is part of the European and Balkan Green Belt. It is a European initiative that connects all the mountains and forests from the northern parts of Finland, across the continent to the south of Greece. The goal is to protect biological corridors, animals to be able to migrate freely, transboundary protected areas to be developed and all nations to work together to protect the environment.

Lake Dojran is part of the Ramsar Convention which unites all rare, endangered and important wet and water ecosystems worldwide.

Lake Dojran as a protected area is part of the NATURA 2000 network. It represents the largest managed network of protected areas in the world. It ensures the protection and promotion of the most important, endangered and rare species and ecosystems in Europe. This does not mean that the Natura 2000 network limits or closes these areas; on the contrary, the network promotes the sustainable development of local communities and their involvement in nature protection.

  1. Invasive species in Dojran

Invasive species are organisms not native to a particular area and cause significant economic and ecological damage in the new location.

Not all non-native species are invasive. For example, most of the crops grown for food, including familiar types of grain, tomatoes, and rice, are not native to those regions. To be invasive, the species must be able to adapt easily to a new area, capable of rapid reproduction, and capable of damaging property, the economy, or native plants and animals in the region.

Many invasive species are introduced into a new region by accident, but a significant number are introduced intentionally due to unreasonable human actions.

Invasive species in Dojran

Nutria

Nutria or coypu (Myocastor coypus) is a large herbivorous, semi-aquatic rodent that often resembles a beaver or a large rat to humans. It originates from the temperate zones of South America, but humans have transported it to North America, Europe, Asia and Africa, primarily for fur farming. Although still prized for its fur in some regions, its destructive feeding and burrowing habits make this invasive species a pest throughout much of its habitat. The nutria were kept throughout the territory of the Socialist Federal Republic of Yugoslavia as part of the fur industry. With the decrease in the demand for fur and the changes in customers’ attitudes towards natural fur, many of the fur farms were closed, and the animals were released. In this way, nutria spread throughout the Balkans, in several parts of the country and in Dojran.

Red-eared slider (Trachemys scripta elegans)

The red-eared slider (Trachemys scripta elegans) is a typical example of an invasive species and how man has unknowingly caused this turtle to be one of the most invasive species in the world today. This water turtle, which naturally inhabits the southeastern parts of the United States as a popular pet, has begun to be sold worldwide. After a few years, irresponsible owners began mass releasing the turtles into local rivers, lakes, ponds and parks. This caused this species to appear all over ecosystems on almost all continents. In Europe, the red-eared turtle is the biggest enemy of the local species of water and swamp turtles, so the sale and transport of this type of turtle in the European Union is prohibited.

Piranhas in Lake Dojran

Very often, irresponsible owners of private aquariums and fish farms aim to eliminate the red piranha species (Pygocentrus nattereri) by illegally releasing the fish into the lake water. This type of fish, because of the local climatic and environmental conditions, cannot survive long in the water; however, their short-term appearance often causes fear among the population.

Releasing and freeing exotic aquatic species kept as pets in Lake Dojran is strictly prohibited!

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