underwater
adj.adj. located, used, or happening below the surface of the water. You use this to describe things like fish, submarines, or hidden rocks.
adj. situated, occurring, or functioning beneath the surface of the water. In a financial context, it describes a loan or mortgage where the debt exceeds the current market value of the asset.
The divers found an underwater cave.
The research team used an underwater camera to film the rare species of shark living near the ocean floor.
The coastal city is investing in underwater barriers to protect its historic harbor from the rising sea levels caused by climate change.
From under (preposition) + water.
From under- + water.
Typically functions as an attributive adjective placed before the noun, though it can also serve as a predicative adjective after a linking verb.
He swam in underwaterHe swam underwaterWhen describing the action of swimming, 'underwater' functions as an adverb and does not require the preposition 'in'.