Some of the most diverse vertebrate assemblages on Earth occur in freshwater communities of the Amazon and the Orinoco River basins. Over 3000 species of fish are estimated to occur in the Amazon Basin alone.
Small river basins are represented by 21 ecoregions, large lakes by 4 ecoregions, small lakes by 7, xeric basins by 3 ecoregions, large river headwaters by 5, large river deltas by 6 ecoregions, and large rivers by 7 ecoregions.
Freshwater habitats include bogs, ponds, lakes, rivers and streams. About 3% of Earth’s water is freshwater, but this includes the water locked up in the ice caps and trapped in rocks and soil as groundwater. Only a tiny fraction (0.014%) is surface water in the form of rivers, lakes and swamps.