A $2.5 million, 1.3-acre stormwater pond that will collect polluted runoff from downtown Bethesda is now complete.

The Stoney Creek Stormwater Management Pond is a six-acre site just south of NIH on the west side of Woodmont Avenue that Montgomery County regards as a key location for capturing runoff from 204 acres of the Bethesda Central Business District and NIH campus. The project also includes a small fountain-like devise to enhance water circulation and other measures for discouraging mosquitoes or other pests.

The pond includes two underground trash collection chambers and new plantings in a forest retention area.

Environmental planners say the project, which began in October 2010, will treat stormwater from parking lots and developed areas that would have otherwise ended up in a tributary of Rock Creek.