Underwater is used to describe things that exist or happen below the surface of the sea, a river, or a lake.
underwater exploration.
水下勘探。
underwater fishing with harpoons.
用鱼叉在水下捕鱼。
Underwater devices are specially made so that they can work in water.
underwater camera equipment.
水下摄影设备。
Something that exists or happens underwater exists or happens below the surface of the sea, a river, or a lake.
giant submarines able to travel at high speeds underwater.
能在水下高速行驶的巨型潜艇。
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。