In Greek mythology, Poseidon and Athena competed over the city/state that eventually became known as Athens.
In Greek mythology, Poseidon's power only extended to the oceans. He would, therefore, have no power to divert rivers.
Hades musical number "My Town" is the only time James Woods has sung in the role. In an interview shortly after the episode premiered, Woods observed that his singing voice did not impress the show's producers.