given the potomac is a legendary risk to the powers that be, post 9/11...it would take an awful lot of work to do anything within commuting distance of the city.
The river is still the major path in and out of the city for flights..
the river is still crossed by many bridges
Many historic/business/important/critical buildings are but a stones throw from the river.
Much of the train/metro parallels the river
If you look closely while traveling the city, you will see all kinds of sensors, cameras, LEO, weapons cached, and military air flights on a regular basis. This is not the DC of old..
Good luck, but I think those in charge will let you know they don't want the risk...
YMMV, feel free to call DHS