South Surin Island (Ko Surin Tai) is one of the two main islands of the Surin archipelago in the Andaman Sea, located about 60–70 km off the coast of Phang Nga Province and separated from North Surin by a shallow channel approximately 200 m wide. The island is known for its quieter environment, limited development, and the presence of the Moken Sea Gypsy village, whose residents maintain a traditional, sea-based lifestyle. Surrounding waters feature healthy coral reefs and slightly deeper snorkeling and freediving areas compared to the north, with notable sites such as Ao Tao (Turtle Bay) and Pak Chak Bay, where sea turtles and diverse reef fish are commonly observed.

Rules for free divers are stricter than other dive sites in Thailand. For example, only dive spots with "blue" buoy are permitted for free diving and this is subjected to the national park 's calendar year rule. Some dive spots requires ONLY short fins. More rules below.

• Visibility: 20–30 m typical in dry season; variable with conditions

• Depth Range: 5–30 m near reefs

• Water Temperature: 27–30 °C

• Water Conditions: Generally calm to gently choppy; currents can vary

• Seasonality: Park open mid-October/November to mid-May; best conditions November–April; closed May–October

• Transportation: Speedboat or long-tail boat from Khura Buri or Khao Lak piers

• Local rules: National park regulations apply. Local free dive instructor is MUST. Free dive training are prohibited.