Underwater bank (5)
I believe the answer is:
shoal
(Other definitions for shoal that I've seen before include "Collection of fish" , "shallow water" , "School of fish" , "Lots of fish" , "Large group of fish - sandbank" .)
I believe the answer is:
shoal
(Other definitions for shoal that I've seen before include "Collection of fish" , "shallow water" , "School of fish" , "Lots of fish" , "Large group of fish - sandbank" .)