Potomac

 is the river that passes through the Capital Wasteland. Its course is generally northwest to southeast, and divides the Fallout 3 map into three regions: to the north and east of the river is Maryland, to the south and west is Virginia, and all of Washington D.C. is on the east side. It empties into the Tidal Basin along with the Anacostia River. Its waters are radioactive, making swimming a hazardous method of crossing; it is best to find an intact bridge or narrow section. Mirelurks are often found in and around it.