A spillway, also known as a water weir, is used to create a nice flow of water at the top of a waterfall or a stream. The water is pumped from the pond or pump vault through a flexible pipe to the weir. The water fills from the highest point and works by evenly spilling out over the lip, creating a nice stream or waterfall. The spillways sometimes have filtration material to help clarify the water. This material helps with water clarification by providing an area for beneficial bacteria to colonize, which will then help clean the water and prevent algae growth.