Mill race
（重定向自Millrace）
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).