Odd bits of beefcake seen in Northern stream (4)
I believe the answer is:
beck
'northern stream' is the definition.
(I've seen this before)
'odd bits of beefcake' is the wordplay.
'odd bits of' indicates alternate letters.
The alternate letters of 'beefcake' are 'BECK'.
'seen in' acts as a link.
(Other definitions for beck that I've seen before include "Poetic gesture" , "Northern stream" , "Fast stream; goes with call" , "burn" , "Stream (N. England)" .)