undertow
noun [ C usually singular ] uk/ˈʌn.də.təʊ/ us/ˈʌn.dɚ.toʊ/
水下逆流;（尤指）退浪，回卷
a strong current flowing underwater in a different direction to the way the water on the surface is moving, especially one that flows away from the land at the same time as a wave hits the beach