Picked up burn in seaside resort (4)
I believe the answer is:
rhyl
'seaside resort' is the definition.
(Welsh seaside resort)
'picked up burn' is the wordplay.
'picked up' shows a homophone (sound like).
'burn' becomes 'rill' (both can mean a stream).
'rill' is a homophone of 'RHYL'.
'in' is the link.
(Other definitions for rhyl that I've seen before include "North Wales resort" , "Seaside resort in Denbighshire" , "Welsh location" , "Clwyd resort" , "N Wales resort" .)