Lake ecosystems

Lakes exist throughout many parts of the world in nearly every type of environment, from forests to mountains and deserts. Though each lake is unique in size, depth, and salinity, or saltiness, the factor that unites most lakes is their rich biodiversity. Lakes are home to a multitude of plants and animals that depend on lakes for their survival. Because of this, lakes themselves have been classified as their own unique ecosystems.

Overview

An ecosystem is the coexistence of all the living and non-living components of a particular environment. The contents of a lake’s ecosystem are directly determined by the salinity of the lake’s water; other contributing factors include the availability of nutrients, levels of dissolved oxygen, pH, depth of water, and temperature. A lake forms from rain, snow, stream water, or ground runoff that collects in a basin. A basin is a ground depression that will eventually hold the water of a lake.

Lakes can be classified in several ways, one of main classifications includes two types of lakes: open and closed. Open lakes have water that constantly flows from and empties into a stream, river, or other waterway. These lakes contain freshwater. Closed lakes do not have water flowing out of them (except through evaporation or ground seepage), but water flows into the lake from different sources such as rain, snow, groundwater, glacier, or rivers. Many closed lakes are made of salt water. The difference between the two occurs because water can only escape a closed lake through evaporation, which leaves behind large amounts of sediment. This sediment causes the water in closed lakes to become salty.

Only a small number of organisms can live in or around saltwater lakes. Most plants cannot survive in saltwater lakes. For example, the Dead Sea, a large saltwater (hypersaline) lake that borders Jordan, Palestine, and Israel, contains such a high salinity that nothing other than microscopic life can survive in it. In 2022, the US Geological Survey launched a major monitoring effort for saline terminal lakes in the Great Basin to track changing water levels, salinity, and effects on migratory birds and other wildlife.

The most diverse ecosystems of animals and plants inhabit freshwater lakes. These lakes serve a variety of purposes for every organism that uses them. Geese may stop to rest on lakes while migrating for the season, while other birds, including ducks, herons, or swans, sometimes return to a certain lake each year to breed or make it their permanent home.

The water of a freshwater lake also provides a fertile environment for plants to grow. Because the ground along a lake’s perimeter is kept enriched with water, plants ranging from reeds to ferns and mosses grow here abundantly. Many lakes are also home to flourishing water lily populations, which float serenely on the water’s surface. These plants provide refuge for animals that live both on land and in the water. Dragonflies, frogs, crayfish, and more take shelter and/or lay their eggs within the safety of reeds and other tall plants along a lakeshore. Numerous other species, such as spiders, salamanders, turtles, and small insects, also inhabit lakes.

Life above a lake is only one part of this ecosystem. The environment beneath the water is just as diverse. Numerous varieties of fish inhabit freshwater lakes, making them popular fishing spots for people around the world. Lakes are home to sunfish, perch, bass, salmon, eels, muskellunge, trout, catfish, pike, and more. The distribution and type of fish living in a lake depend on the location of the lake.

At first glance, lakes do not appear to change much over time. However, lakes are ever-changing, as they are confined to life cycles just like any other ecosystem on Earth. They are born and die every day. The death of a lake begins at the bottom, where runoff sediment, dead algae and other plants, and the remains of animals collect to form hard, rock-like structures. As these solid masses grow larger on the floor of a lake, water is displaced, which causes the lake to shrink slowly. The shores of the lake gradually recede toward the center until the formerly large and thriving ecosystem becomes a small, nearly lifeless swamp or marsh. Eventually, these small bodies of water are covered over with earth.

When left to nature, a lake’s transition from birth to death can take thousands of years. This figure can vary depending on the amount of salinity and types of sediment in the lake, but the process is usually extremely gradual. Human pollution of the water, however, can speed up the death of a lake. Introducing unnatural objects such as paper and plastic products to a lake’s water increases the rate at which sediment collects at the lake’s bottom. This can reduce the time it takes for a lake to die from hundreds or thousands of years to several decades. In the United States, the Environmental Protection Agency’s (EPA) 2022 National Lakes Assessment, published in 2024, found that 50 percent of lakes were in poor condition for phosphorus, 47 percent for nitrogen, and microcystins were detected in half of the lakes.

Dead lakes leave behind diverse ecosystems, and scientists eagerly study the sites of former lakes to learn much about these ecosystems. By digging up dry lake beds or the areas around small wetlands, paleontologists can discover almost perfectly preserved fossils of animals ranging from simple, ancient bacteria to the full skeletons of dinosaurs. By studying the number of layers of sediment on top of these fossils, paleontologists can determine how old the specimens are and how long ago the lake and its ecosystem went extinct. It is the fate of all lakes on Earth to fill in and die, but new lakes are forming elsewhere simultaneously. These will eventually become homes for new and diverse ecosystems that will inhabit them for the next few thousand years. A 2026 Nature Communications study found that climate extremes such as heatwaves and extreme rainfall can intensify eutrophication (a condition where water bodies have a high concentration of algal blooms that degrade water quality, possibly because of high levels of nutrients such as nitrogen and phosphorus) and harmful algal blooms, even in lakes that are not highly nutrient-rich.

Bibliography

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Han, Long, et al. “Relationship between Lake Salinity and the Climatic Gradient in Northeastern China and Its Implications for Studying Climate Change.” Science of The Total Environment, vol. 805, 2022, no. 150403, doi:10.1016/j.scitotenv.2021.150403. Accessed 14 Apr. 2026.

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Wang, Chenyu, et al. “Climate Extremes Intensify Global Lake Eutrophication by Increasing the Stress Resistance of Harmful Bloom-Forming Algae.” Nature Communications, vol. 17, 2026, no. 2859, doi:10.1038/s41467-026-69529-3. Accessed 14 Apr. 2026.

Wetzel, Robert G. Limnology: Lake and River Ecosystems. Academic Press, 2001.