Swimming in water after ending in brook, jumpers say? (8)
I believe the answer is:
knitwear
'jumpers say?' is the definition.
(jumpers are a type of knitwear)
'swimming in water after ending in brook' is the wordplay.
'swimming' indicates an anagram.
'after' means one lot of letters go next to another.
'ending in' suggests the final letters.
The last letter of 'brook' is 'k'.
'in'+'water'='inwater'
'inwater' anagrammed gives 'nitwear'.
'nitwear' after 'k' is 'KNITWEAR'.
(Other definitions for knitwear that I've seen before include "stockings, perhaps" , "Woollen clothes" , "sweaters, for example" , "'Woolly jumpers, socks etc (8)'" , "Cardigans, jerseys, etc" .)