Pohick Bay is part of the Potomac River and is located South of the beltway. It is a Northern Virginia Regional Park and has nice facilities for launching canoes and kayaks.
As you head north after launching, you head back into the marsh. Yesterday it felt like a wildlife tour. We saw 3 bald eagles and more osprey than we could count. There were also several great blue herons and 7 or 8 great egrets. All in all it was very pleasant. The jet skis can't get back in there.
The area is affected by the tides so pay attention to the tide schedules. It seemed like a difference of a foot to a foot and a half difference in water depth. At high tide it was wonderful. At near low tide, the hydrilla was a nuisance. It had grown up since the last time I was there.
All in all it was still a nice place to paddle.
Nice facilities for launching canoes and kayaks. Campground in the park. Plenty of parking.
$5 to launch a boat. If you are from out of the area, there is a charge to enter the park.
I 95 South from DC. Take the Lorton Exit and head toward Rt 1. Its pretty well marked. Right on Rt 1 and go to the top of the hill and turn left. Its well marked all the way.