undertow
n[sing]
current below the surface of the sea, moving in the opposite direction to the surface current, esp the current caused by the backward flow of a wave breaking on a beach (海面下与海面水流呈反向流动的)回流(尤指浪拍岸退回形成的)
caught in an undertow 碰上回流
The pull of the undertow can drag swimmers out to sea. 近岸回流的冲力能把游泳的人涌到海里.