Swimming movement of animal crossing river with oarsman? (12)
I believe the answer is:
breaststroke
'swimming' is the definition.
(thesaurus)
'movement of animal crossing river with oarsman?' is the wordplay.
'movement of animal crossing river' becomes 'breast' (I can't justify this - if you can you should give a lot more credence to this answer).
'with' says to put letters next to each other.
'oarsman?' becomes 'stroke' (I've seen this before).
'breast'+'stroke'='BREASTSTROKE'
Can you help me to learn more?
(Other definitions for breaststroke that I've seen before include "Natant style" , "Adam Peaty's swimming style" , "What swimmers may do" .)