Freshwater

The biome of lakes, rivers, streams and freshwater wetlands, set apart from the Marine biome by very low salt content and, unlike the ocean, by a tight two-way link to the surrounding land: a river or lake's chemistry, temperature and flow are shaped directly by the watershed draining into it. Ecologists commonly split it into lotic systems, flowing water such as rivers and streams, and lentic systems, standing water such as lakes and ponds, alongside freshwater wetlands, marshes and swamps that sit at the boundary with dry land and flood only seasonally or permanently at shallow depth. Freshwater habitats cover under one percent of the Earth's surface, yet hold a disproportionate share of the planet's species: a large fraction of all known fish species and much of its amphibian diversity live nowhere else, concentrated into a tiny share of available habitat. Because freshwater bodies exist on every continent and across every climate, from tropical floodplain to Arctic lake, this biome carries no single characteristic temperature or rainfall range the way a climate-defined biome does; its unifying trait is fresh water itself.