I don’t have details at hand, but I can tell you 5 places very close-in on the Potomac to launch a kayak.
1. Washington Sailing Marina, just south of the airport. There’s a ramp that can pay a launch fee for.
2. Also Washington Sailing Marina, there’s a free ramp to the left of the entrance that enters behind the docked sailboats. It’s theoretically maintained by the Park Service, but it’s pretty grungy at the best of times.
3. Roaches Run, or the “duck pond”, just north of the airport on the west side, where all the limos park waiting for passengers to call. You can park there free, and there’s a small launch point right over the curb.
4. Belle Haven Marina, a mile or two south of Wilson Bridge in Alexandria off GW Parkway. You can pay to launch from their ramp ($6 for trailer-less launch last time I looked). Probably the most interesting place to kayak, with the marsh.
5. Also Belle Haven Marina, but free, and questionable. Staff told me a couple years ago (new management now), that I could just carry/drag my boat over to the rocks to the north of the bathrooms and drop in there. It’s a public park.
I’ve only tried #4. The rest is an adventure waiting to happen. Good luck!