(water version of dodge ball)
Assemble two teams and designate one as the "Offense" and the other as the "Defense" and position them at opposite ends of the "shallow" part of the pool. A referee with a stop watch on deck is the leader.
Supply soft rubber balls or small beach balls. The offense team tries to hit the defense players. An offense team member can retrieve balls, but he must return to the starting position before throwing again. Defensive players must get out of the pool when hit. After all the defense players have been hit, the referee notes the elapsed time and the teams change roles. The team that stays in the water the longest before being hit is the winner.