 If the water level in your pond is suddenly rising, take a look at the spillway. Its job is to control the maximum depth of the pond and direct the outflow to an area that won't compromise the integrity of the pond structure. A spillway that's not maintained is headed for trouble. Tim Mattson is a pond consultant and author. He says in a natural spillway where the excess water leaves through a stream-like channel, plants will grow in. But if they become overgrown, it can cause problems with water drainage.