Freshwater Ecosystems and Ocean Productivity

Rivers rank among the most productive and biodiverse freshwater ecosystems, shaped by the volume, seasonality, and sediment load of their flow as much as by climate. The Amazon River, discharging roughly one-fifth of all the freshwater that enters the world's oceans, supports the highest freshwater fish diversity of any river system on Earth, with well over 2,000 described species including the Amazonian manatee, the pink river dolphin, and the formidable arapaima, one of the largest freshwater fish in the world. The Mekong River, flowing some 4,350 kilometers from the Tibetan Plateau through China, Myanmar, Laos, Thailand, Cambodia, and Vietnam, sustains the world's largest inland fishery, supporting the livelihoods of tens of millions of people across the basin, and is home to the critically endangered Mekong giant catfish and one of the last populations of Irrawaddy dolphins, though the river's ecology has been significantly altered by a rapid expansion of hydropower dams over recent decades.