I second Yambag's advice. If the weather is decent, I would hit Fletcher's boat house (pretty sure they are open through end of Oct) and rent a row boat and row upriver as far as you can. You'll want to find current and breaks from the current. An hour before you need to be on the road, start floating down river back to Fletchers. If you want to keep fishing while you float back, target the shoreline current breaks along either side of the river.
6wt and some streamers will give you a shot at smallmouth bass, schoolie striped bass if you get lucky, and big ol' catfish, blue, channel, and maybe a bullhead. A floating line will suffice but a sink tip or full sink might not be a bad idea to try if presenting with a floating line isn't producing. An 8wt might not be a bad idea either if you have one just in case you hook a decent blue cat.
Overall though, fishing will probably be slow at most spots in and around DC. But if you hit fletchers, you'll at least be on a boat. In DC. Where it doesn't feel like DC.
If you have access to a smallish cooler, bring it. In my opinion, a properly stocked cooler and a boat, no matter the size, and regardless of number of handled fish, makes for a fine way to spend a few hours. Hell, bring a friend. Other than the stray paddle boarder or random sculler, you'll probably be the only person on the water.
Let us know how it goes!