Some fun ways to learn about water safety
Rope, long stick
Run through the basics of water safety, where not to swim and why etc. Then practise some simple life saving by marking off a pond / lake for a beaver to 'drown' in. then get the others to practise throwing them a rope / reaching with a stick & pulling them to the bank. The important thing to stress to the beavers is not to put themselves in danger; i.e lay flat on ground when reaching so they don't over balance.