A canal connecting the Potomac and Anacostia Rivers was a feature of the original L’Enfant plan for Washington. It took a while to build, but then remained in use until after the Civil War, by which time it had turned into an open sewer.
The land on which it was built was reused, parts with an actual sewer underneath, some entirely filled in. The surface is used mainly for roads, but a section near the waterfront was turned into Canal Park.
The other end of the canal was under Constitution Avenue and ended at the Lockkeeper’s House. You can read about the house at the Washington Post (log in through DCPL if you don’t have an account!) And if you scan forward to 1:37 here, you can hear (and see) me pontificate on that building.