Young people have pole placed in river (5)
I believe the answer is:
teens
'young people' is the definition.
(I've seen this in another clue)
'pole placed in river' is the wordplay.
'pole' becomes 'n' (abbreviation for North, as in North Pole).
'placed in' means one lot of letters goes inside another (I've seen this in other clues).
'river' becomes 'tees' (River Tees).
'n' inserted inside 'tees' is 'TEENS'.
'have' acts as a link.
(Other definitions for teens that I've seen before include "Adolescence" , "The years 13 to 19" , "Adolescent years" , "Years 13-19" , "children" .)