Before a long time, lake lost because of this? (7)
I believe the answer is:
leakage
'because of this?' is the definition.
The definition suggests a singular noun which matches the answer.
'before a long time lake lost' is the wordplay.
'before' means one lot of letters go next to another.
'a long time' becomes 'age' (an age is a period of time).
'lost' indicates anagramming the letters.
'lake' with letters rearranged gives 'leak'.
'age' after 'leak' is 'LEAKAGE'.
(Other definitions for leakage that I've seen before include "Escape of liquid - or private information" , "Unwelcome flow" , "That which seeps out" , "Unwanted discharge of fluid" , "Liquid/gas accidentally lost" .)