A detention basin/pond temporarily stores stormwater runoff. The basin is designed to manage stormwater runoff by storing it and releasing it gradually until completed drained.
Unlike a detention basin, a retention basin or pond is designed to permanently hold water. Retention basins are commonly used when the groundwater is near the surface of the ground. A retention basin will not have an outlet structure. The water collected by a retention basin will either infiltrate into the ground or evaporate.
The advantage of a retention basin over a detention basin is the higher removal of pollutants. Retention basins can also serve as an aesthetic or recreational amenity, as well as a habitat for some wildlife. They will become their own ecosystem.