So I went kayaking on the Blackwater River in Virginia, a Nature Conservancy Preserve.
I put in at the Rte 620 bridge (southeast side of bridge; there is a posted sign to the right as you turn into the pull-off; go straight along a plowed field and there's a put-in by the river at the other end... not posted).
I could see right away why they call it the Blackwater River; dark tea colored water. It was flatwater for the most part. I went upstream first. Had to climb over several trees that had fallen across the entire river. After about a mile, I gave it up and paddled back to the put-in. Then I went downstream for about two miles before I began running into the same situation -- fallen trees blocking the way. Thus ended the adventure.
This could be a nice paddling river, if it were cleaned up a bit; plenty of water flow, tupelo cypress trees, and feels like you're in the Louisiana Bayou. One note of caution however: ticks abound along the riverside.