water columnnoun [ C ]
uk/ˈwɔː.tə ˌkɒl.əm//ˈwɑː.t̬ɚ ˌkɑː.ləm/specializeda vertical section of water from the surface to the bottom of the sea, a lake, a river, etc.:
The water column is a way of describing the different features found in seawater at different depths.