Separate the hall one area is the beach and other is the sea. Leaders have a set of flags and discuss (quietly) which flags they are going to raise. Beavers need to know what the flags mean. The Leaders are the flag poles (a good space between them, leaders can alter the space between themselves even while beavers are swimming/surfing in the sea) a quick way to get some out (are they paying attention to the flags). For example the Leaders could raise the safe to swim in the sea flags, the Beavers need to ensure that they swim in the sea area between the flags (if they stray outside or get the flag instructions wrong they are out).
Flag Print outs; balloons (inflatables); two leaders or young leaders.
Red/Yellow Flag - Swim in the sea with inflatables (balloons)
Red/Yellow Flag & Windsock - Swim in the sea without inflatables
Red Flag - Stay on the beach and make pretend sand castles
Black & White Flag - Surf/Body board in the sea.