Part of the larger 64,000 square mile Chesapeake Bay Watershed

Rock Creek is a 65 square mile watershed in Adams County, PA. At the confluence with Marsh Creek, Rock Creek becomes the Monocacy River, which then drains to the Potomac River and finally to the Chesapeake Bay. The RCW is a headwaters drainage area because no stream flows into it. Tributaries flow into Rock Creek include Whites Run, Littles Run, Stevens Run, Chicken Run, Plum Run, and Lousy Run. The Rock Creek and its tributaries flow through a variety of landscapes: farmland, villages, the Gettysburg National Military Park, commercial and industrial centers, and woodlands. Rock Creek serves as the eastern boundary of Cumerland Township and separates it from both Straban and Mt. Joy townships. The watershed includes all of Bonneauville, a portion of Gettysburg, and parts of Straban, Mt. Joy, Cumberland, and Mt. Pleasant townships. Communities such as Lake Heritage, Twin Oaks, Hunter's Crossing and the Links are also located within the watershed.

While the health and function of the Chesapeake Bay may not be of obvious concern to Rock Creek Watershed municipal governments and citizens because it is so geographically far away and comprises a very different ecosystem, the function and health of the Bay ecosystem is a direct reflection of the health and function of each of its tributary watersheds, including the Rock Creek Watershed.