Form of dam (4)
I believe the answer is:
weir
'form of dam' is the definition.
(I know that weir is a type of levee)
This is the entire clue.
(Other definitions for weir that I've seen before include "Madagascan primate" , "Low dam across a river" , "Low dam built across a stream" , "Small dam to regulate water flow" , "Structure for raising water level in river" .)