John Quincy Adams used to go for nude morning swims in the Potomac.
We really need a President who will reinstitute this tradition.
I grew up a stone's throw from the Potomac 10 miles downriver from D.C. and man, you really don't want to swim anywhere in the Potomac near D.C. Below the city it's a polluted mess, above is waterfalls that routinely kill people.
That said, I used to swim in the river sometimes. Unavoidable when you are sailing Lasers whilst young and restless. It was also a bit of a rite of passage on our swim team to swim across to the M.D. side and back.
Also, a friend of mine spotted and called in a corpse in the river one time.