In order to prevent any debris from escaping from the skimmer basket when your pump is turned-off, there is a door that closes the skimmer system-off This door is called the skimmer weir. Like the skimmer, the skimmer weir adjusts to the water level in your pool on its own It floats just on top of the water so that it can always collect floating dirt and materials When you need to replace your skimmer basket or clean it out, you can completely shut this skimmer weir This stops any water from entering the skimmer Materials: PVC, nylon, and ABS Size: 5 to 20 inches