Low dam (4)
I believe the answer is:
weir
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">low dam</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for weir that I've seen before include "River flow regulator" , "Feature of river" , "Dam on a stream to control water level or flow" , "Low dam built across a stream" , "Madagascan primate" .)