Our dermatologist has recommended Bullfrog products for years. The gel products, (not the creams) are nearly waterPROOF. For my ultra pale, practically translucent-skinned family, the Bullfrog gels do not sweat off, do not swim off, do not wear off until we shower with soap and scrub off.
That’s why she recommends it… it doesn’t need to be reapplied multiple times for most people, other than the back of your hands or if you wash your face. And it dries completely & quickly, so it won’t get into a youngling’s eyes if they rub them.
I would think if it won’t come off romping at a pool or water park, it’s not gonna come off in the ocean. Idk if it has the reef safe designation or not… but I’d feel fine using it.
I second (third?) the suggestion of long-sleeved spf-rated clothing. One of our boys was so burn-prone that’s we would still make him wear long-sleeved T-shirts even with sunscreen. This was before there was spf-rated clothing, though…
I personally think we need to worry more about all the pollutants being pumped into the oceans and rivers from multiple industrial sources, before we worry about the comparatively minute amounts from tourists’ sunscreen. But that’s just me.