Mine worker taking sheepdog by river (7)
I believe the answer is:
collier
'mine worker' is the definition.
'sheepdog by river' is the wordplay.
'sheepdog' becomes 'collie' (collie is a kind of sheepdog).
'by river' becomes 'r' (abbreviation. I am not sure about the 'by' bit.).
'collie'+'r'='COLLIER'
'taking' acts as a link.
Can you help me to learn more?
(Other definitions for collier that I've seen before include "Painter" , "Ship carrying coal" , "unable to avoid contact with mine" , "Pitman" , "Miner; coal ship" .)