Lake that feeds the Truckee River (5)
I believe the answer is:
tahoe
'lake that feeds the truckee river' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tahoe that I've seen before include "Lake/desert resort on the California-Nevada border" , "Lake in Sierra Nevada mountains" , "US lake" , "Mountain lake" , "Nevada/California lake" .)