Thai authorities have closed the popular island Koh Tachai to visitors, blaming high tourist numbers for damaging its ecosystem. The problems included litter and food waste, gasoline from tour boats leaching into the water and damage to coral, with overwhelming numbers of tourists to blame The island will be closed from October 15, 2016, but you won't be able to visit the island before as Thailand shuts down all marine national parks from mid-May to mid-October, during their monsoon season.