underwater
adjective, adverb uk/ˌʌn.dəˈwɔː.tər/ us/ˌʌn.dɚˈwɑː.t̬ɚ/
B2 在水下（的）;（尤指）在海面下（的）
under the surface of the water, especially under the surface of the sea
an underwater camera (= a camera that you can use underwater) 水下摄像机
Some species of turtle can remain underwater for 24 hours. 有些种类的海龟能在水下呆上24小时。