A dam is a man-made barrier that impounds (i.e., collects and confines) water. Dams can serve various functions, such as to control or store runoff, provide drinking water, provide recreational opportunities and more. In Fairfax County, most dams are constructed earth with a concrete control structure. There are thousands of small stormwater management facilities in the county that utilize dams to store excess stormwater runoff from our land in a dry pond or a wet pond. Water in a dry pond drains completely after a rain event, while a wet pond will have a permanent pool. A few larger dams, such as Lake Accotink, provide recreational opportunities or provide a source of drinking water, such as the Occoquan Reservoir.