Skimmer weirs are important to getting the best circulation in your pool or spa. The most common pool and spa weirs are “floating rings” or “flapping doors”. A weir floats at the water level and causes water to speed up as it passes over the weir which increases the suction and helps skim debris off of the surface of the water. The debris passes into the skimmer and gets trapped in the skimmer basket so that it does not continue on to the pump and filter.
The weir also keeps the bugs and leaves from returning into the pool or spa, particularly when the pump is not running. And it protects the pump from sucking air by helping maintain the water level undisturbed over the skimmer itself.
If your skimmer weir is broken or missing it is a good idea to replace it. Though your pool or spa will still function and circulate without a weir, you will have a better looking, cleaner body of water with the best circulation, if your replace the weir. It is super easy to do and relatively inexpensive.