There are definitely snakeheads in the Potomac. There was an article last years in the Washington Post magazine that I saved about the snakeheads. I also found a link to a preview of it online:
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Anyway, what the article said is that when you actually hook into one they put up a great fight. The problem is that they are very good at telling apart a real meal apart from a lure, so they're hard to catch. There are guides around here that will help you get into the snakeheads, but there's no guarantees about actually catching one. It did mention something about looking for spots on the water where there seems to be a circle of a bunch of little fish swimming at the top of the water in the springtime. That's little snakeheads and the parent should be undeneath protecting them. Cast into the circle or right behind it and pull your lure through and you might have a better chance of getting one.
If you do manage to catch one you definitely need to report it to DNR and don't release it. It will definitely be killed either way, but if they let you keep it I hear it's actually a pretty good eating fish.