The Waterhive were creatures composed of water. In their true form, they resembled limpets with a single eye. They could take over the body of a drowned being. The body would thus be preserved, although the eyes of their host would become "pearly", forcing glasses to be worn. They infiltrated the high ranks of the Navy in order to send sailors and their loved ones to their watery graves. Their plan was to use the living drowned as human incubators for their larvae. This failed when the Tenth Doctor reduced the hive to atoms. (PROSE: The Feast of the Drowned)
Waterhive were one of the explanations the Doctor gave on Arcopolis for ghosts. (PROSE: The Eyeless)