The Pool at Courtyard by Marriott Washington Capitol Hill/Navy Yard
The pool at Courtyard Washington Capitol Hill/Navy Yard is recommended by professional reviewers. Out of 2 professionals tracked on TripExpert, 2 recommended the pool, like Oyster and Fodor's.
Courtyard by Marriott Washington Capitol Hill/Navy Yard 
Oyster
Fodor's
Oyster "It's a nice enough place -- clean, comfortable rooms; gym and business center; even a pool with Jacuzzi -- but the neighborhood is sleepy, and a bit isolated from the rest of D"
Fodor's "Rooms are large and nicely done in "Federalist" blue and gold, and amenities include an indoor pool"
