Riverside pool (4)
I believe the answer is:
bank
I believe this is a double definition.
'riverside' is the first definition.
(I've seen this before)
'pool' is the second definition.
(thesaurus)
(Other definitions for bank that I've seen before include "River side - pool" , "6D 5A [TUBE STATION]" , "Land beside river" , "Financial institution - riverside" , "Edge (of river) - tier (of oars)" .)