Something that exists or happens underwater exists or happens below the surface of the sea, a river, or a lake.
双语例句
例： giant submarines able to travel at high speeds underwater.
能在水下高速行驶的巨型潜艇。
例： Some stretches of beach are completely underwater at high tide.
海滩上有些地方在涨潮时会完全被水淹没。