A water blockage (3)
I believe the answer is:
dam
This clue could be a double definition.
'a water' is the first definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'blockage' is the second definition.
(I've seen this before)
Can you help me to learn more?
(Other definitions for dam that I've seen before include "Water barrier, quite mad" , "Reservoir barrier" , "eg Aswan" , "Wall restraining water" , "Mother - barrier" .)