epipelagic

This term is a specialized scientific descriptor used primarily in oceanography and marine biology. It carries a neutral, technical register and is rarely encountered outside of academic papers, textbooks, or environmental reports. It specifically identifies the sunlight zone, distinguishing it from deeper, darker layers like the mesopelagic or bathypelagic zones.

Because it describes a specific biological and physical environment, it is almost always used as an attributive adjective modifying nouns such as zone, region, species, or community. It is not used in casual conversation to describe general water or swimming areas.