Lake and river rose alarmingly (9)
I believe the answer is:
reservoir
'lake' is the definition.
(reservoir is a kind of lake)
'river rose alarmingly' is the wordplay.
'alarmingly' is an anagram indicator (I've seen this in other clues).
'river'+'rose'='riverrose'
'riverrose' with letters rearranged gives 'RESERVOIR'.
'and' is the link.
(Other definitions for reservoir that I've seen before include "Large water store" , "Source of water supply" , "Man-made lake or tank" , "River rose (anag.)" , "Lake for collecting and storing water" .)