It's getting to be summer and therefore time to have a swim party. If you have your own pool, excellent, your back garden will be a perfect spot, if not, the local plunge is the next best thing. Public pool or private spot the party can be the same; obviously setting up games at home would be easier than at the public pool and the combatants of any game or contest will be easier to control in a private setting. The point is to get the kids and their parents to the pool and spend the day having fun and cooling off at the same time.
Set up a picnic in either spot, your local party supplies shop can help with those arrangements; blankets are good for the lawn, whereas paper table cloths and napkins may be a better bet at the public pool. For games at your swim party you will obviously want swimming races with some party favours, pocket money toys, as prizes. Diving contests are fun, but for the older kids and perhaps the adults too, a way to separate the men from the boys may be in order. It might be nice to quiet the loudmouth who thinks he is the local Tarzan and to do that I have just the game.
You will need some long bungee cords, probably half the length of the pool, find out from the university swim team coach where he gets his. These bungees are used for strength training by all the top swim teams. Find a way to anchor them to the end of the pool, or just have a person hold on to one end. Attach the other end to the swimmer. The guy that can stretch the bungee and swim the farthest wins, or the one who can keep the cord stretched for the longest amount of time gets the prize. Either way, whoever participates in this particular torture will without exception be worn out for the rest of your swim party.