The Similan Islands lie approximately 100 kilometres northwest of Phuket in the Andaman Sea. In 1982, this 128 square kilometre area was declared a marine national park, and in recent years the group of nine small islands (Similan is derived from the Malay sembilan, and means nine) has become one of the leading attractions for visitors to southern Thailand. The islands are renowned among divers for their rich coral reefs, clear waters and pristine beaches. The best diving months are between December and May when the weather is fine and underwater visibility at its best. The Similans offer over 200 species of hard coral, many more soft corals, hundreds of colourful fish species, and tens of thousands of other marine organisms which make their homes on the reefs.