One of Thailand 's most popular island tourist sites . Koh has a beautiful natural environment, many sandy beaches, coral reefs and coastal lagoons covered island is also quite famous waterfall . Diving is one of the most popular activities on Koh Samui , mostly carried out in the vicinity of Turtle Island , where the seabed visibility of about 20 to 40 meters , there is a rich variety of marine life , including pike , perch, tortoiseshell , etc., there when even see whale sharks , but also appreciate the rock surface covered with sponges , sea anemones and corals. Ko Phangan is another diving hotspot , where in addition to views of barracuda , whale sharks endures, sometimes encounter stingrays and other marine life. Koh Samui is also popular sea kayaking adventures , visitors can participate in local adventure group canoe to Ang Thong Marine National Park in the island group adventure tours , watch one of the natural caves , beaches, coral reefs and rock formations .