river

A river is a natural flowing watercourse, typically freshwater, that moves from higher to lower elevations through a definite channel. It collects water from precipitation, groundwater, and tributaries, forming a drainage basin that discharges into a larger body such as a sea, ocean, lake, or another river. Rivers can be perennial, flowing year-round, or intermittent, with flow that varies seasonally or with drought.

The river's course often changes along its length. In upper reaches, steep gradients promote erosion and rapid transport of sediment; downstream, meanders develop across floodplains, creating features such as cut banks, point bars, and sometimes oxbow lakes. Rivers transport water, sediment, and dissolved minerals, shaping landscapes through processes of erosion, transportation, and deposition. Discharge measures the volume of water passing a point per unit time and varies with rainfall, snowmelt, and human withdrawals.

Rivers sustain diverse ecosystems and provide services for people. They support aquatic and riparian habitats, enable fish migration, and supply water for drinking, irrigation, and industry. Rivers also enable navigation, recreation, and hydroelectric power, while floodplains and deltas support productive wetlands.

Management challenges include pollution, sedimentation, overuse of water, and the construction of dams and levees. Integrated river basin planning seeks to balance ecological health with human needs. Climate change can alter flow regimes and flood risks, affecting water availability and ecosystem resilience.