Hoover or Grand Coulee
I believe the answer is:
dam
This clue is a double definition.
'hoover' is the first definition.
(I've seen this in another clue)
'grand coulee' is the second definition.
(I've seen this in another clue)
(Other definitions for dam that I've seen before include "eg Aswan" , "Flood barrier" , "Barrier to contain the flow of water" , "Female parent; obstruction" , "River restraint" .)