The Opal Sea is a body of water located on the planet Pelagia Prime. In late 2379, William T. Riker and Deanna Troi shared their honeymoon on the Opal Sea. As a wedding present, Jean-Luc Picard allowed Riker and Troi to use his yacht, the Calypso II, for the duration of the honeymoon. (TTN novel: Taking Wing, ST - Tales from the Captain's Table short story: "Improvisations on the Opal Sea: A Tale of Dubious Credibility")