Not sure if this launch is allowed by the Park Police or not (although a Park Police vehicle drove by me as I was putting my boat on the car and did not stop), but here it goes. On Ohio Drive (paid parking, $2/hr) at a small point at the bridge in front of Jefferson Memorial, there is a very small sandy area partially submerged. I put in here last weekend, was a very nice paddle along the park. Just north is Lincoln Memorial, then Kennedy Center, Watergate Hotel, then Georgetown all on east side.
Across river Arlington and TDR island on west as you paddle north.