A player is picked to be "it". The player who is "it" then swims to one side of the pool and turns their back to the other swimmers who are lined up in the water on the opposite side of the pool as "it".
Players choose a color and keep it to themselves (To make it easier you can limit the color choices, like to the colors of the rainbow). "It" begins to call out colors one at a time. If a player's color is picked then the player tries to make it to the other side of the pool as quietly as they can.
If "it" hears a player swimming then "it" turns around and tries to tag the player before they swim back to the side of the pool where they started.
If "it" turns around and the players still have a hand on the side of the pool then "it" returns to the side of the pool where they started and starts calling out colors again.
If "it" catches a swimmer then the swimmer becomes the new "it".