One person is the "it." They stand in the middle of the pool with their eyes closed. The other players start at the shallow end of the pool and try to swim to the other end of the pool without being tagged. When you reach the other end say "Mission Impossible." Then swim back without being tagged and say
"Mission Completed." If you are the first one to be tagged, then you are the next "it." If no one is tagged the last person to complete the mission is the next "it."