Try the RNLI website. They have excellent downloads, and booklets you can send off for, for safety at the sea side.
For waterways safety, try the Canals and Waterways Trust. They too have downloads, puzzles, games etc, and booklets you can send for.
As we are by the sea, we use the lifeboat things more than the others.
We've just done the water safety badge through games. For the flags, we did something rather like Captain's Coming, for which they ran around then I held up an A4 card flag and they had to show an agreed action e.g. for black and white checks they wobbled on a surfboard, for red and yellow they swam and for red they built a sandcastles because they were on the beach not in the water. For the sequence of rescue techniques, I wrote each on a card and sixes put them in the order they thought was least risky then we discussed the real order (and why) and they acted one for other sixes to guess. With our families, we walked along the canal and river one evening towards the end of the badge and at various stops the girls had to answer a question or explain something to their adult. Parents were very impressed with what they had learned. The Canal and River trust sent 2 great speakers who held everyone's interest and brought little sticker books. The RNLI also have visiting speakers. We wrote safety rules on posters and the Brownies had to draw an appropriate picture that showed they understoood the rule.
We invited a very lovely lady from the RNLI to run a session...
She was brilliant - she showed a few slides, and brought life jackets to try on, some beach warning flags, and played a game about what do do if you're drowning!
It was a great evening - all it cost us was a donation to RNLI (which we collected on the night - and we got a lovely Thank You certificate!)
We also had someone from the RNLI come and do an evening with us. I sent her the badge details beforehand and she tailored the evening to that.We watched a short film, looked at the different flags and what they mean, dressed up, did some activities that matched some of the badge criteria and I followed it up the following week with the bits we didn't have time to cover. She left us some posters to help finish off. The girls loved the evening and the feedback from parents was very good. We asked parents for a donation and we added a donation from the unit too. I can fully recommend them and so would my Brownies.
We used the acronym DROWN:
Check for Danger
Rules/signs/flags - read and obey.
On your own? Don't swim.
Wait for 999 if someone's in trouble
Need to help? Then do so safely, without getting in the water.