Water game, outdoors.
Equipment: none.
Formation: teams
Divide the group into teams of 8-10 players.
Set up a 'monster' relay where every player has a role. Some swim through shallow water, some through deep water. Have some do cartwheels through shallow areas, while others swim with one hand in the air.
The design of the relay depends on your waterfront set-up and the abilities of your swimmers.
End the relay by having one player piggyback a teammate across a finish line, located in shallow water.