Lake and river rose chaotically (9)
I believe the answer is:
reservoir
'lake' is the definition.
(I know that reservoir is a type of lake)
'river rose chaotically' is the wordplay.
'chaotically' is an anagram indicator.
'river'+'rose'='riverrose'
'riverrose' is an anagram of 'RESERVOIR'.
'and' acts as a link.
(Other definitions for reservoir that I've seen before include "Source of water supply" , "Man-made lake to store water" , "Store for water etc" , "Artificial lake" , "Man-made lake of stored water" .)