Most wastewater treatment plants and industrial facilities discharge their effluent into the nearest available body of surface water such as a stream or river. The mixing zone is the localized area in the receiving stream within which the mixing, dispersal, or dissipation of the effluent can be detected. For example, cooling water discharges from power plants typically create a mixing zone in the receiving stream where the temperature is higher than the ambient background temperature of the stream waters. Environmental regulations usually require that the mixing zone be limited in size and not create a nuisance or hazardous conditions.