Rising lakes? Get a sailing vessel (5)
I believe the answer is:
sloop
'a sailing vessel' is the definition.
(sloop is a kind of sailing vessel)
'rising lakes?' is the wordplay.
'rising' is a reversal indicator (going up in a down clue).
'lakes?' becomes 'pools' (pool is a kind of lake).
'pools' backwards is 'SLOOP'.
'get' acts as a link.
(Other definitions for sloop that I've seen before include "Vessel with a single mast" , "Single-masted sailing boat" , "Sailboat" , "Type of sailing boat" , "One-masted sailing boat" .)