World Rivers and Lakes

Earth is commonly described as the water planet, yet the volume of water available for terrestrial life is extraordinarily small. According to the United States Geological Survey, less than three percent of the water on Earth is fresh, and the overwhelming majority of that freshwater is locked in glaciers, polar ice sheets, and deep groundwater. Only about three tenths of one percent of Earth's total water takes the form of accessible surface freshwater, and that sliver is divided among rivers, lakes, reservoirs, and wetlands. Every civilization, crop, forest, and freshwater species depends on this narrow layer of liquid.

Rivers are flowing systems that transport water, sediment, nutrients, and heat from high ground to oceans, inland seas, or terminal basins. Lakes are standing bodies of water that collect and store what rivers, rainfall, springs, and glaciers deliver. Together they form a planetary circulatory system that recharges soils, cycles carbon and nitrogen, and carries the chemistry of continents to the sea. The United Nations Environment Programme describes freshwater ecosystems as the most diverse per unit area on Earth.

These freshwater systems do practical work at every scale. Municipal drinking water, irrigation for food production, industrial process water, inland navigation, hydroelectric generation, commercial and subsistence fisheries, tourism, and recreation all depend on rivers and lakes. They also anchor ecological functions that are difficult to replace: floodplain nutrient cycling, groundwater recharge, climate regulation through evaporation, and habitat for migratory birds, amphibians, fish, and countless invertebrates.

This survey is one of several companion pieces. Readers interested in the saltwater portion of the hydrosphere may turn to the World Oceans and Seas article, while those curious about the living communities that freshwater sustains will find relevant material in Biomes and Ecosystems. The account below concentrates on the rivers and lakes themselves, their geography, their governance, and their future.