A
mill race,
millrace or
millrun is the current of water that turns a
water wheel, or the channel (
sluice) conducting water to or from a water wheel. Compared to 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 (or headrace), and the race leading away from the wheel is called the
tail race (or tailrace).