Crossword Genius

Water creature caught in a small boat (4)

Ross

I believe the answer is:

crab

I'm a little stuck... Click here to teach me more about this clue!

'water creature' is the definition.
'crab' can be an answer for 'creature' (crab is a kind of creature). I am not sure about the 'water' bit.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for crab that I've seen before include "accidentally caught in a row?" , "Sourpuss < to wreck" , "The constellation Cancer" , "A sea creature; an apple" , "Stalk-eyed crustacean" .)

I've seen this clue in the Evening Standard.
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