How to Stop Your GoPro Headstrap From Falling Off in Water?

In December, I'm in Mexico for waterskiing. I got a GoPro a while back and thought it would be pretty fun to film my skiing with it. However on impact when falling into the water, I'm worried my GoPro will fall of and I'll loose it in the lagoon.

Will my Headstrap be secure enough, or will I need to buy other equipment to keep it from sinking? Thanks:)

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