Mu Ko Similan National Park

Mu Ko Similan National Park, established in 1982, protects a granite island chain in the Andaman Sea about 60 km off Khao Lak, plus the later additions of Koh Bon and Koh Tachai to the north. The western sides of the islands are all smooth boulders — arches, canyons, and swim-throughs like Elephant Head Rock — while the eastern sides slope in classic hard-coral gardens. Leopard sharks rest on the sand, mantas and whale sharks pass Koh Bon and Koh Tachai, and turtles nest on beaches such as Donald Duck Bay. Famous Richelieu Rock lies farther north inside neighboring Mu Ko Surin National Park, sharing the same seasonal regime; liveaboards thread both parks.

The rules that bind divers

The park closes annually for the southwest monsoon — roughly mid-May to mid-October — and all diving happens in the open season, mostly by liveaboard and speedboat day trips under park-registered operators. Visitors pay national park entrance fees plus per-dive fees, collected by operators. Koh Tachai's beach was closed to tourism in 2016 for recovery, and specific dive sites open or close by park order. Fishing, collecting, and anchoring on coral are prohibited — boats use park moorings — and overnight island stays have been curtailed in recent years, with day-use rules on the beaches.

Fees & permits: Park entrance fee (foreigner rate higher) plus diving fees per day, collected by operators; fees and camping rules change by park order.