A lot row, ending in lake (5)
I believe the answer is:
spate
'a lot' is the definition.
(I know that lot can be written as spate)
'row ending in lake' is the wordplay.
'row' becomes 'spat' (a spat is a disagreement or argument).
'ending in' suggests the final letters.
The final letter of 'lake' is 'e'.
'spat'+'e'='SPATE'
(Other definitions for spate that I've seen before include "Sudden increased quantity" , "Sudden forceful flow" , "Flood; sudden burst" , "Suddenly got a lot" , "A sudden flood or rush" .)