Millrace

A mill race, millrace or millrun, mill lade (Scotland) or mill leat is the current of water that turns a water wheel, or the channel (sluice) conducting water to or from a water wheel. Compared with the broad waters of a mill pond, the narrow current is swift and powerful. The race leading to the water wheel on a wide stream or mill pond is called the head race, and the race leading away from the wheel is called the tail race.

Wikipedia →