Does everyone have pool parties to celebrate the end of the school year? Or is that a regional thing?
If you are planning a pool party or graduation party, remember that there are direct links to some fun challenges in the sidebar that are perfect for this type of event. One in particular, Ice Cold Colors, is played IN the pool.
Another fun idea for good swimmers? Have an underwater scavenger hunt. Create teams and give each team a different list of items to find. Use items that sink, along with a couple of floating things. Your lists could include things like a metal spoon, a golf ball, a sponge, a plastic cup and an old CD.