Rock Creek is a free-flowing tributary of the Potomac River, which empties into the Atlantic Ocean via the Chesapeake Bay. The creek is 32.6 miles (52.5 km) long,[1] with a drainage area of about 76.5 square miles (198 km2). The last quarter-mile (402 m) of the creek is affected by tides.[2]
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The creek rises from a spring near Laytonsville in Montgomery County, Maryland, and joins the Potomac near Georgetown and the Watergate in Washington, D.C. Beginning in the Derwood–Rockville area in Maryland, the creek flows through Rock Creek Regional Park southward to the D.C. boundary. About 9 miles (14 km) of the creek flow though Rock Creek Park in Washington, where it is fed by several small creeks — Piney Branch, Pinehurst Branch, Broad Branch, Soapstone Branch, and Luzon Branch — and numerous storm sewers.
The Maryland portion of the watershed comprises the second-largest watershed in Montgomery County, about 60 sq mi (160 km2). About 21 percent of the creek's watershed is in Washington. Total land usage in the watershed is 896 acres (3.63 km2) of wetlands or water, 22,272 acres (90.13 km2) of residential and commercial areas, 15,488 acres (62.68 km2) of forest or grasslands, and 10,304 acres (41.70 km2) of agricultural areas. The creek has a fairly steep gradient, with rapid changes in elevation. The man-made Lake Needwood is located on the creek, north of Rockville.
In Maryland, most of the northern Rock Creek watershed has good to excellent water quality, according to studies conducted by the county government. In 2004, to preserve water quality in partially developed areas, the county imposed restrictions on development (i.e., designation of a "Special Protection Area") in parts of this sub-watershed.[3] The southern portion of the Maryland watershed is highly urbanized. The majority of this portion of the creek and its tributaries has poor water quality.[4] The county is managing several stream restoration projects throughout the watershed.[5]
The D.C. segment of Rock Creek also has poor water quality. In addition to typical urban stormwater pollution problems such as runoff from streets and other impervious surfaces, the creek has high bacteria levels due to combined sewer overflows (CSOs).[6] The D.C. government, which has a stormwater discharge permit issued by the United States Environmental Protection Agency, is improving its stormwater management to improve water quality in Rock Creek.[7] In 2009, the District of Columbia Water and Sewer Authority began a project to replace portions of the combined sewer with separate storm sewers. The project, which is expected to eliminate the CSO-related problems in the creek, is scheduled to be completed in 2011.[8]
In 2006 the National Park Service completed a project to remove or bypass eight fish barriers in the creek. Restoration activities included adding a fish ladder to bypass the 1905 Peirce Mill Dam, modifying historic fords, and removing abandoned sewage lines and fords. The effort is designed to restore American shad, river herring, and other migratory fish to the creek and their historic upriver spawning grounds.[9] It is estimated that 2 million fish migrate up the creek each year.
(Listed in order from the mouth upstream)
| Potomac River system Cities and towns | Bridges | Islands | Tributaries | Variant names District of Columbia | Maryland | Pennsylvania | Virginia | West Virginia Streams shown as: Major tributaries • subtributaries • (subsubtributaries) • (subsubsubtributaries) |
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Lakes and reservoirs
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