Richard from DC on 6/7/2019 1:51:46 PM:
I live in Bethesda and bike that stretch all the time. The last campground that I can remember is at Swain's Lock, so it seems right that there's nothing after Potomac. You probably wouldn't want to camp any closer to the city anyway for safety reasons and besides, once you get inside the Beltway, it tends to get buggy and swampy.