https://phys.org/news/2018-11-palau-sunscreen-coral.html

A spokesman for President Tommy Remengesau said there was scientific evidence that the chemicals found in most sunscreens are toxic to corals, even in minute doses.

He said Palau's dive sites typically hosted about four boats an hour packed with tourists, leading to concerns a build-up of chemicals could see the reefs reach tipping point.