Washington, D.C., is bordered on the west by the Potomac River, which divides D.C. from Virginia. The Anacostia River runs through its east side. D.C. also has several islands in the Potomac, such as Theodore Roosevelt Island, which has a number of walking trails and is often visited by locals. You can also check out Kingman Island, a man-made island in the Anacostia River, which is the site of a popular bluegrass festival each summer.