The Western Sea was a body of water on the planet Pacifica.
Lwaxana Troi, en route to Pacifica for a conference in 2365, proclaimed to the bridge crew of the USS Enterprise-D that she would marry William Riker on the shore of the Western Sea. She made the announcement while under the influence of the Phase, and to the surprise of Riker. The wedding she spoke of did not take place. (TNG: "Manhunt")