Surfacewater

Surface water refers to water that exists on the surface of the Earth, including rivers and streams, lakes and ponds, wetlands, reservoirs, canals, and coastal and open-ocean waters. It is distinct from groundwater, which is stored underground. The distribution and availability of surface water are governed by climate, topography, geology, and land cover, and it forms a major part of the hydrological cycle. Surface water is replenished primarily by precipitation and inflow from upstream sources, and it is removed by evaporation, infiltration, withdrawals, and downstream flow. Flows in rivers and streams may be perennial or intermittent; lakes store water for varying periods; wetlands act as buffers and filters for nutrients and sediments.

Surface water supports drinking water supplies, irrigation, energy production, transportation, recreation, and industrial processes. Ecologically, it provides habitat for many aquatic and riparian species. Water quality in surface bodies depends on nutrients, sediments, contaminants, temperature, and dissolved oxygen.

Management of surface water involves monitoring discharge and quality, controlling pollution, and balancing competing demands among municipalities, agriculture, industry, and ecosystems. The close coupling of surface water with groundwater, climate variability, and human infrastructure means changes in land use, rainfall, or dam operation can alter availability, timing, and flood risk. Protection efforts may include watershed planning, pollution controls, sustainable withdrawal limits, and restoration of wetlands.