"Witness” director Peter (4)
I believe the answer is:
weir
'witness director peter' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for weir that I've seen before include "Low dam across a river" , "Structure for raising water level in river" , "Madagascan primate" , "Small dam built across river to regulate flow" , "feature of some rivers" .)