Mu Ko Chang National Park

Mu Ko Chang National Park (Thai: อุทยานแห่งชาติหมู่เกาะช้าง) is located in Ko Chang District, Trat Province, eastern Thailand. It is a marine national park with an area of 650 square kilometres (250 sq mi), including more than 52 islands. The most notable island within the archipelago is Ko Chang. Established in 1982, it is an IUCN Category II protected area with coral reefs.

Ko Chang National Park islands are far from the river streams of the mainland, and so the sea water around the islands, especially further south, near the Ko Mak island, is very clear.

Source https://en.wikipedia.org/wiki/Mu_Ko_Chang_National_Park