The freshwater biome is a low-saline, or sweetwater, aquatic biome that covers one fifth of the earth's surface. Streams, rivers, swamps, bogs, ponds, lakes, ditches, puddles, and canals comprise the tributaries of the freshwater biome. Animals and plants in this biome might reside along the bank, beneath open water, on the surface of the water, or move between water and an adjacent biome.

Precipitation and melted ice feed the freshwater biome. It's responsible for all the world's drinking water, and therefore must be protected and conserved. The associated ecosystems depend on the freshwater biome to complete their reproductive cycle, protect them from harsh sunlight, or provide nutrients. In a still body of water, like a lake, the littoral zone is located near the shore or bank, and the limnetic zone is out in the open water. These zones generally have different flora and fauna.

Plants of the freshwater biome might grow along the bank, float on the water's surface, or attach to an underwater floor of rocks, sediment, or sand. Some plants have wide, flat leaves or air-filled capsules that keep them bobbing on the surface. Tiny sprigs of algae float and multiply freely as a significant biomass. Other species have strong or sticky roots that attach to the bottom to keep them secure in fast-moving water. Cattails, watercress, and assorted grasses grow on marshy banks where their roots receive lots of moisture but aren't washed away by the current.

The animals have adapted to swim, skim, or wade through the freshwater biome. Mammals like badgers, otters, and minks build their homes near the water and feed on fish. Amphibians and reptiles, among them toads, frogs, alligators, crocodiles, salamanders, and newts, spend part of their lives underwater, as eggs and tadpoles, and part on the ground as mature adults. Fish, such as trout and bass, are a necessary part of the ecosystem. They feed on plentiful insects like water beetles, mosquitoes, and dragonflies. Some insects, like skaters, are designed to skim over the surface of ponds. Certain spiders can even take bubbles of air with them underwater to breathe.