A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground and vanishes from the surface. Rivers originate as precipitation on high ground that flows downhill into creeks and streams. Water seeping out of the ground through saturated-soils adds to this volume. Together, these flows merge into rivers.
Deltas are found on the lower reaches of rivers, where the flow of water spreads out and slows down, depositing sediments into expanses of wetlands and shallow water. Coastal deltas are found around the world while examples of inland deltas include the Niger in Mali or the Pantanal in South America.
The importance of healthy rivers
Rivers give life-sustaining services to people. Throughout human history, rivers have served as important sources of drinking water, food and irrigation for crops. Rivers have played an essential role in the growth of civilizations as highways for transportation, commerce and sources of energy.
Rivers and deltas provide critical habitat for fish and other freshwater animals such as amphibians and molluscs. Thousands of species rely on healthy water flows for their survival. River waters also recharge lakes and transport fertile sediments that enrich floodplains and marshes.
Threats to rivers
Growing human populations and increased demand for water by industry and agriculture is reducing both the quantity and quality of available water in rivers. The rising use of irrigated crops for food production and the reduced flows caused by dams means that little or no water reaches the sea from rivers in the Middle East, parts of South Asia and North Africa.
Climate change is impacting water cycles. In some dry regions, declining precipitation is reducing runoff and water flows. In Monsoonal climates, mountain areas are at risk from increased flooding due to intense rainfall events.
Our work protecting river deltas
We are working to maintain the benefits provided by wetlands in the face of growing pressures on rivers and deltas.