Obstacle races in a swimming pool.
Pool, plus any of the following. Kayaks, bricks, rings, socks, golfballs, floats etc.
Teams of four compete in obstacle relays. The following are examples, but most ideas seem to work.
Straddle kayak and paddle with hands. Pick up an extra team member each length until all 4 are on the boat, then race to finish.
Collect brick or ring from the bottom (point A), swim with it and put it down at point B, then swim to end and tag teammate. They collect from point B and put it in point A, tag teammate and so on until team has finished.
Swim with a golf ball balanced on a float, passing ball and float to teammate to tag.
Collect golf ball in sock from bottom, put it on and swim to end. Pass to teammate, who will put it on and swim to collect another golf ball and sock. Final swimmer will finish with sock and ball on both hands and feet.