sea water coastal sea water Coastal sea water is sea water that is adjacent to a coast. ENVO ENVO:00002150 The limits of what qualifies as "adjacent to" vary greatly. This should be defined on a data level and is left intentionally fuzzy here. The label is "coastal sea water" rather than "coastal water" as some large lakes are often said to have coasts. coastal ocean water coastal oceanic water coastal seawater coastal water