Great swimmer worried over extremes of climate in Canada (8)
I believe the answer is:
cetacean
'great swimmer' is the definition.
'cetacean' can be an answer for 'swimmer' (thesaurus). I am not certain of the 'great' bit.
'worried over extremes of climate in canada' is the wordplay.
'worried' becomes 'ate' (something worrying may eat someone up).
'over' says the letters should be written in reverse.
'extremes of' means to remove the middle letters (only the letters at the extremes of the word).
'in' is an insertion indicator.
'canada' becomes 'CAN' (common abbreviation eg in sporting competitions).
'climate' with its middle removed is 'ce'.
'ate' back-to-front is 'eta'.
'eta'+'ce'='etace'
'etace' put into 'can' is 'CETACEAN'.
Can you help me to learn more?
(Other definitions for cetacean that I've seen before include "Generic name for whale, dolphin or porpoise" , "Encase cat with mammals like whales and dolphins" , "Member of the animal order containing whales and dolphins" , "One swimming" , "Large marine mammal" .)