I spent more than a few hours going after one snakehead that made its way inside an urban stream last year and took residence in a deep pool for a while. This guy was easily 10 pounds and 30 inches long too. I went there with the intention of finding one after I read about how the MNCPPC and Montgomery County DEP guys shocked up two adult snakeheads out of NW branch, far upstream from the Anacostia (just below Route 29, below a water fall/natural blockage). So I put that together and hit another stream with a blockage preventing further upstream migration and there he was.
So... I went back a half dozen times. First with flies, then with top water, then with crank baits, worms.. finally went back with a 5 gallon bucket full of small bluegill and still didn't get him. He rose up for air three times right in front of me one day too. After that he may have split because I only saw him on two different trips. I did however catch a lot of bass during my numerous snakehead hunts.
I talk to a lot of regulars on the Potomac and the fast water up by Chain Bridge holds them well, in addition to the more popular bass haunts inside Mattawoman Creek. The anglers around Chain Bridge like to throw broken back rapalas, bass color, the 3 to 4 inch size. They will actually sight cast for them too. The snakeheads give away their position when they come up to gulp air ( to fill air bladder) just like a tarpon. When they do... it's game time. But all I know is that just because you know where one is, doesn't mean he's going to play.