Movement of water round wet rocks (8)
I believe the answer is:
undertow
'movement of water' is the definition.
'undertow' can be an answer for 'movement' (undertow is a kind of movement). I am not sure about the 'of water' bit.
'round wet rocks' is the wordplay.
'rocks' indicates an anagram.
'round'+'wet'='roundwet'
'roundwet' with letters rearranged gives 'UNDERTOW'.
Can you help me to learn more?
(Other definitions for undertow that I've seen before include "Wet round (anag.)" , "Strong current opposed to that on surface" , "Submarine movement" , "Current, unforeseen" , "awkward current" .)