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 "Special Protection Areas") in parts of this sub-watershed. The southern portion of the Maryland watershed is highly urbanized. Most of this portion of the creek and its tributaries have poor water quality. As of 2018 the county has completed several stream restoration projects throughout the watershed, and has additional projects planned or under construction. 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 leaking sewer pipes and combined sewer overflows (CSOs). The D.C. government, which has a stormwater discharge permit from the United States Environmental Protection Agency, is improving its stormwater management to raise water quality in Rock Creek. In 2009, the District of Columbia Water and Sewer Authority began a planned two-year effort to replace portions of the combined sewer with separate storm sewers, and so eliminate CSO-related problems in the creek. As of 2021, the bacteria levels in the creek remained dangerously high due to the leaking sewer pipes, even during dry weather, and the public has been warned not to wade into the creek. Fish species observed in Rock Creek and its tributaries include eastern blacknose dace, bluntnose minnow, yellow bullhead, satinfin shiner, swallowtail shiner, longnose dace, and American eel. Restoration projects In 2006, the National Park Service finished a project to remove or bypass eight fish barriers in the creek by 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. An estimated two million fish migrate up the creek each year. The D.C. government completed a restoration project on the Milkhouse Run and Bingham Run tributaries in 2013. As of 2014, ongoing restoration projects in the watershed include the Broad Branch and Klingle Run tributaries. Tributaries (Listed in order from the mouth upstream) In D.C. Dumbarton Oaks Normanstone Creek Klingle Valley Creek (also called Klingle Creek, Klingle Run) Piney Branch Melvin Hazen Valley Branch Broad Branch Soapstone Branch Luzon Branch Milkhouse Run Bingham