Northern runner in St Helens occasionally (4)
I believe the answer is:
tees
'northern runner' is the definition.
'tees' can be an answer for 'runner' (River Tees). I'm unsure of the 'northern' bit.
'st helens occasionally' is the wordplay.
'occasionally' indicates alternate letters.
'st'+'helens'='sthelens'
The alternate letters of 'sthelens' are 'TEES'.
'in' is the link.
Can you help me to learn more?
(Other definitions for tees that I've seen before include "Stockton's river" , "Northern river" , "River of north-east England" , "Golfer's equipment" , "Middlesbrough's river" .)