River

The river biome, known to ecologists as a lotic freshwater system, covers flowing fresh water from small headwater streams down to wide lowland channels, unified by the continuous one-directional movement of water that shapes everything living in it. Current speed, water temperature, dissolved oxygen and channel structure change markedly from a river's cold, fast, rocky headwaters to its warmer, slower, sediment-laden lower reaches, so a single river can host very different communities along its length, from cold-water trout in the mountains to catfish and freshwater mussels in the lowlands. Rivers are the biome's own kind of freshwater life, distinct from the still-water lake biome, and they link terrestrial, wetland and, ultimately, marine biomes together as they carry water, sediment and nutrients from mountain to sea.