T-Shirt Relay
This funny twist on the classic relay requires racers to start by wearing a large T-shirt over their bathing suit. The teen dives or jumps into the pool and swims to the other side, where a team member is waiting. The swimmer gets out, takes off the T-shirt, and the waiting team member puts it on. Once the T-shirt is totally on (you can have a judge to ensure this), that team member dives in and swims across where the next team member is waiting. You can play this with two to four (or even more) players on each team.
Water Hose Limbo
You can still have fun with water even if you don't have a pool. Put some fun music on a boom box and hold a water hose at shoulder height. Place your finger through the stream to create a strong, steady line of water. Have players do the limbo under the water stream. Anyone who gets wet is out. Lower the water line each round until a winner remains.
Ping Pong Scramble
Before this pool game, use a permanent marker to write numbers from one to five on a bunch of plastic ping pong balls. Place two or more buckets or laundry baskets on the side of the pool and have players line up in teams next to their bucket or basket. Dump the ping pong balls in the center of the pool. Players jump in and scramble to find and place as many ping pong balls in their bucket as they can. The players can only carry one ball at a time. At the end, add up the numbers on the balls to see which team got the highest score.
Water Balloon Squat
This classic relay game requires no pool, but will get every player wet. To start, divide players into two equal teams. Fill a water balloon for each player, and some extra just in case. Place water balloons in two piles at the start line and two chairs each about 20 feet from the line. Players must grab a water balloon, run it to the chair, then place it in the seat, sit on it until it pops, and run back to the start line, where the next player grabs a balloon and does the same. If anyone drops the balloon while running, she must return to the start line and grab a new balloon. The team that pops all the balloons first is the winner.