Weir

A weir (also known as a lowhead dam) is a small overflow-type dam commonly used to raise the level of a river or stream. Weirs have traditionally been used to create mill ponds in such places. Water flows over the top of a weir, although some weirs have Suice gates which release water at a level below the top of the weir. The crest of an overflow spillway on a large dam is often called a weir.

The adjacent image shows the wier at Coburg Lake, Victoria (Australia) after heavy rain.