Lakes and ponds range in size from as little as a few square yards up to thousands of square miles. Some ponds can be seasonal, while lakes are generally much longer term. These bodies of water sometimes have just a few species and are often far from one another. Lakes and rivers feature three subcategories. The littoral zone is located near the shores of lakes and ponds and is home to algae, snails, insects, crustaceans and amphibians. It is the warmest of the zones within the freshwater biome, as it is always in very shallow waters. The limnetic zone is situated near the surface in the open water and is populated by plankton, small organisms close to the bottom of the food chain, and by freshwater fish. The profundal zone comprises the deepest waters of lakes and ponds, with much cooler temperatures than the other two zones.
Streams and rivers in the freshwater biome are more common than lakes and ponds. They start at places such as lakes, melting snow, springs and other headwaters. They generally flow from one of these water sources until they reach another body of water or the ocean. Characteristics of streams and rivers change while they flow from source to destination, becoming warmer and lower in elevation. Freshwater fish such as trout often live near the steam's or river's source. As the river or stream becomes deeper and wider, it hosts a larger diversity of species, including algae and other aquatic plants. Closer to the mouth of the stream or river where the waters are not as clear due to the sediments picked up along the journey, there are more hardy fish which do not need much oxygen to survive. These include carp and catfish.
The third of the freshwater biomes is the wetlands, where standing water is found. These include swamps and marshes, whose waters are home to aquatic plants, black spruces and cypress. Animals include reptiles, birds and amphibians.
