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The Northwest Branch is one of two major free-flowing tributaries to the tidal Anacostia River. Its confluence with the Northeast Branch, north of the town of Bladensburg, forms the tidal river. The subwatershed boundaries of the Northwest Branch are generally outlined by Olney-Sandy Spring Road to the north, New Hampshire Avenue and Adelphi Road to the east, University Boulevard and Georgia Avenue to the west, and the southern edge of Hyattsville to the south. Seventy-four percent of the subwatershed is in Montgomery County, with 18% and 8% in Prince George's County and the District of Columbia, respectively.

Dominant Land Uses: The largest land uses, by area, in the Northwest Branch subwatershed are residential (52%) and forest cover (22%); agricultural land use and parkland comprise 9% and 7%, respectively.

Physical Characteristics: The Northwest Branch subwatershed (exclusive of the tributary drainage from Sligo Creek) is 26,808.3 acres (41.9 mi2) in size and approximately 17% impervious. Elevations range from 500 feet at the subwatershed divide to five feet at its confluence with Northeast Branch. With an average mainstem gradient of 0.39%, the Northwest Branch flows from the Piedmont physiographic province into the Coastal Plain.

Biological Characteristics: The Maryland Department of the Environment has designated the lower portion of Northwest Branch as Use I waters; the subwatershed area upstream of East-West Highway is classified as Use IV, recreational trout waters. High quality aquatic habitat and fish and macroinvertebrate populations exist in the headwaters of Northwest Branch, upstream of Bonifant Road. From this point downstream in the subwatershed, the condition of mainstem aquatic biotic populations steadily deteriorates to a minimum of 69% and 53% of the reference condition for macroinvertebrate and fish, respectively (Cummins et al., 1991).

Condition Summary: The headwaters of the Northwest Branch subwatershed are largely semi- rural with some agricultural and low density residential land uses dominating; there are also large tracts of undeveloped land. Twenty-two percent of the subwatershed remains forested, and 45% of the stream miles have an adequate riparian forest buffer (300-foot total width). The lower portions of the watershed are more urbanized with higher residential densities and some commercial development. Some of the best water quality conditions in the Anacostia are found in the upper portions of Northwest Branch, and these waters support among the healthiest macroinvertebrate and fish populations in the entire Anacostia; the stream above Route 410 (East-West Highway) is classified as an MDE Use IV recreational trout stream. However, water quality and aquatic habitat deteriorate in the lower stream reaches due to higher density development, associated stormwater impacts, stream channelization downstream of Queens Chapel Road and a corresponding degradation of instream aquatic habitat and dependant biota.

To get involved in protecting your Anacostia subwatershed contact The Neighbors of Northwest Branch