Mag Brook, also sometimes referred to as the Mag Stream, is the continuation of Hall Dike and becomes a tributary of the River Holme, which it joins in Magdale near Steps.
Traditionally, the stream formed part of the boundary line between the districts of Honley and South Crosland and the valley through which it runs was known as the Mag Brook valley or Mag Valley.
The stream also feeds a mill dam at Magdale.