Creature in raging Thames river (7)
I believe the answer is:
hamster
'creature' is the definition.
(hamster is a kind of creature)
'raging thames river' is the wordplay.
'raging' indicates an anagram.
'river' becomes 'r' (abbreviation for river).
'thames' is an anagram of 'hamste'.
'hamste'+'r'='HAMSTER'
'in' acts as a link.
(Other definitions for hamster that I've seen before include "The arms (anag)" , "Small pet rodent with pouched cheeks" , "Kind of rodent with cheekpouches, often a pet" , "Oddly, the arms of a rodent" , "Common pet rodent" .)