There are more than 100.000 species of freshwater animals. Although about 70% of the Earth is covered with water, only 3% of it is freshwater; that is, 0,01% of the planet’s total surface area.
Many freshwater lakes were formed during the last ice age. Their deep, quiet waters and dense vegetation banks provide habitats to rare species of plants and animals. Only a few habitats can compete with the beauty of lakes.
There are two extremes of freshwater lakes: They are either very rich in nutrients or very poor. Nutrient-rich lakes are called eutrophic lakes, and nutrient-poor lakes are called oligotrophs. Nutrient-rich lakes are found in areas where the soil has a soft structure, which continually crumbles, giving way to mineral water with nutritional value. In addition, the water collection area of these lakes is also rich in nutrients.
These nutrients infiltrate the lake and influence its living world. Fertilizers used in agriculture also supplement the nutrient content. In cloudy water, the sun’s rays penetrate the lake only shallowly, making plant growth more intense on the surface and on the waterfront.
The last ice age, which took place 10.000 years ago, left most of its traces in these regions.
Nutrient-poor lakes are rarely surrounded by farmland. These lakes contain little vegetation and a small number of fish. In the bays away from the unfavorable climate, dandelion and other shore plants provide food and protection to fish and waterfowl. Until today, mountain lakes have been less affected by pollution.
Each species, from the smallest crayfish to the captor fish, is an important element of the lake’s ecological balance. In the sand of the shore washed by the water of the lake live Turbellaria, species of Chrysoperla and Patella, snails shaped like a taler. In clean water the sun’s rays penetrate the water deeply, creating an environment conducive to the development of the frog-and-nib grass.
The middle of the lake is populated by huge groups of tiny creatures, such as those of the genus Bacillaria. Here is the home of the crayfish species as well, which is the favorite prey of rainbow trout. In nutrient-rich lakes live a wide range of insects and larvae, such as dragonflies and Dytiscus maginalis, the great diving beetle.
The larger lakes attract many visitors from the North Pole during the cold season, who winter here. These are less sensitive birds, such as the small duck, the summer goose, and the short-beak goose.
Other well-known visitors are brown-headed ducks, as well as small swans and singing swans. Birds with stilts search for their food, such as shells, worms, and insects, on the banks of the lakes.
In the deeper waters, the small plunder, some duck species, and the large Gavia stellata dive into the water to catch crayfish and small fish.
If the lake is surrounded by forests, here both sedentary and migratory birds find food. Wren and Paridae populate the pine and oak forests, but we can sometimes also encounter herons, who sit motionless on the shore hunting a frog or a bird’s chick. The field owl, the hawk, the white codfish, and the traveling eagle occasionally search for their prey on the lake shore, and the fishermen-eagles build their nests in old trees on the banks of the quiet lakes.
Freshwater lakes provide a home to many mammal species, both to those who, thanks to their rich supply of food, live on the banks and to their predators.
The otter builds its burrow on the shore of lakes, so it can supply it with water; the Eurasian water shrew hunts aquatic insects and small fish, and the water rat feasts in dense vegetation. Rodents, baby birds, and frogs attract foxes and weasels.
Wild ducks live near lakes, dams, and lagoons in rural and urban areas. Males have a green head, a yellow beak, and a brown chest while females are completely brown.
These ducks look for plants and small animals in the water as their food. They use their beaks to sense the surface of aquatic bodies.
When they’re on the ground, they’re looking for seeds, insects, and flowers.
White herons live in swamps and wetlands around the world. These freshwater sources provide important habitats for many birds. White herons are migratory birds and can grow up to a meter tall.
These are mollusks that have three stages in their life cycle: eggs, larva, and adult. Adult snails have soft bodies and hard shells. These snails have triangular tentacles on their heads. Its eyes are at the bottom of the tentacles.
Most snails measure less than two centimeters. They can often be found on aquatic plants and rocks near the water. These animals feed on plants and are hermaphroditic.
Freshwater turtles are one of the oldest reptiles and did not evolve much in the 200 million years they lived on Earth.
These turtles are also at risk of extinction because the illegal trade with them is very popular. They are also threatened by pesticides and the destruction of their habitat.
They are the stage of amphibian larvae, such as frogs. They have small eyes, a short, oval body, a broad tail, and no external gills.
Once their metamorphosis is complete, they look like a frog. The tadpole stage can last from two weeks, one or two months, up to three years.
It is a rare endemic amphibian from the valleys of the Mexican Basin. Unlike most amphibians, they do not undergo a metamorphosis process and feed on small fish and their young. It is currently in danger of extinction due to the degradation of its environment.
The American beaver is one of two living beaver species, the other being the Eurasian beaver. It is the second largest rodent in the world, after the South American capibara, and can reach weights of up to 50 or 60 pounds, 23-27 kg. American beavers are animals with compact trunks and short legs, palmed legs, and with broad and flat tails covered with scales. American beavers are constantly building dams from sticks, leaves, mud, and twigs that provide these oversized rodents with deep water habitats to hide from predators. The dams also provide winter shelter for other species and create wetlands. Beavers are a key species for the ecosystem, their presence greatly affects the landscape and the food network wherever they live.
They live in rivers, lakes, wetlands, and swamps. Although they sometimes reach a length of 4 feet and weigh more than 20 pounds, most of them are less robust. Aided by the toes, the otter can sink to about 30 meters and swim at a speed of 7 miles per hour.
They’re pretty strange animals. They can be defined as a mixture of a duck, a beaver, and an otter. Males are poisonous.
The platypus hunts underwater, so it swims with the help of its legs and tail. They can stay underwater for up to 2 minutes and are native to Australia.
It is one of the largest reptiles in North America, reaching 18 feet in length. They are found in freshwater in the southeastern United States.
It is distinguished by its dark and round muzzle, its dark color, and the absence of visible teeth when the mouth is closed.
It is a snake that lives in the mangrove roots of the Everglades, Florida, and in certain regions of North Carolina and Louisiana in the United States.
It’s the most poisonous big snake in this area.
Multiplication of algae.
Nitrogen and phosphorus are important nutrients, but in excess, they exert a destructive effect. It infiltrates the water of the lake on the shores treated with fertilizers and causes the algae to multiply excessively. Thus, an algae carpet is formed on the surface of the water that stops the passage of the sun rays, and eutrophication. By day, algae release oxygen, but at night they consume all the oxygen dissolved in water, thus preventing the breathing of aquatic plants and animals.
The industrial world annually releases millions of tons of harmful acid substances into the atmosphere, which reach back to the ground in the form of acid rain. These substances not only cause the destruction of trees but also end up in the water of lakes. Acidic water intoxicates aquatic plants, birds, and mammals.