If there are just two players, this game is a race. With four or more players divide into teams and make it a relay.
Each team has a beach ball that the players must move from one end of the pool to the other by pushing the ball with their noses and forehead. If they touch the ball with their hands or any other part of their body they must go back to where that took place and start again.
When the player reaches the end of the pool the next player will do the same until one team is the winner.
Good swimmers can play by swimming in the deep end of the pool or the length of the pool. For a game with non swimmers, play in the shallow end.