The Cache Creek Dam on the South Fork of Cache Creek, five miles (8 km) downstream from Clear Lake, was built to increase Clear Lake's capacity and to regulate outflow for downstream users of Cache Creek water. The dam was later modified to include a 3 MW hydroelectric plant. The stream has a relatively small capacity, less than a quarter of the amount the dam is able to release. There is a rock ledge a mile and a half downstream of Clear Lake, called the Grigsby Riffle, near the bridge on State Route 53. This ledge restricts the amount of water that can flow through at that point. The limited capacity of the stream means that it takes a very long time to drain excess flow from Clear Lake, increasing the chance of flooding around the lake. The bottleneck is seen as a backup to prevent flooding downstream and Yolo County is prohibited from increasing the capacity of the channel by the Gopcevic and Bemmerly Decrees.