Fish in river turned right into bottom of boat (8)
I believe the answer is:
mackerel
'fish' is the definition.
(mackerel is a kind of fish)
'river turned right into bottom of boat' is the wordplay.
'river' becomes 'cam' (I've seen this before).
'turned' says the letters should be written backwards.
'right' becomes 'r' (common abbreviation).
'into' means one lot of letters goes inside another.
'bottom of boat' becomes 'keel' (I've seen this before).
'cam' written backwards gives 'mac'.
'r' placed within 'keel' is 'kerel'.
'mac'+'kerel'='MACKEREL'
'in' acts as a link.
(Other definitions for mackerel that I've seen before include "Common food fish" , "that's fishy" , "Oily food fish" , "Banded food fish" , "A fish; sort of breeze, sky" .)