Easy, gang....Airbus380 is correct, there is a lagoon right next to DCA RWY 1. The George Washington Parkway is on the spit of land that divides it from the Potomac River. The lagoon is a federal waterfowl sanctuary. I've seen 8-10 Blue Herons at once standing in it at once, while driving by on the parkway.
If you're driving southbound on the Parkway, just after you pass I-395 you'll notice that there's water on both sides of you. On the left is Gravelly Point park, with its spotting area and soccer fields, then the Potomac River. On the right is the lagoon/ waterfowl sanctuary, which indeed often has fishermen at its banks. There's a small pull-off area for cars to park; cabs often wait there for some reason.
Just as you reach the end of the lagoon, DCA is on the left. Props using the crosswind runway--15/33?--fly right over it on the way in.
Need a new airline paint scheme? Better call Saul! (Bass that is)