A stream that gains water from ground water flow. These streams are typical of humid climates where water tables are high. The discharge of an effluent stream can be sustained by ground water flow for long periods of time between runoff-producing rainfall or snowmelt. Effluent streams generally increase in discharge downstream and contain water throughout the year. The opposite is an influent stream.

stream or portion of a stream that receives some water from groundwater discharge because the stream's elevation is below the groundwater table. (Compare Influent stream.)

a stream flowing below the water table and receiving water from the groundwater.