We just returned from a great cave diving expedition to Ang Thong National Park in the Gulf ofThailand. The aim was to locate the cave that feed the saltwater lagoon on Koh Thali Nai, this saltwater lagoon is in the center of the island and surrounded by sheer cliffs. The lagoon is a saltwater cenote and fed by an underground cave to the sea.
We found this map by some French cave explorers locating the entrance on the eastern side of the island. The main problem would
be locating the cave and predicting the flow in the cave, as at sometimes the cave would turn into a syphon, pushing you into the cave making it difficult or impossible to exit if the cave is impassable. Syphonic conditions are also dangerous as you need more gas to exit and sediment stirred up will washed into the cave with you.
We quickly located the seaward side entrance not far from the beach, with a high flow running out of the cave just one hour before low tide, as the lake was emptying into the sea. The cave was wide nearly 5 metres across but only 70 cm high making sidemount diving the only choice. After a primary tie off on the surface we descended to the entrance. With 3-4 knots current flowing out of the cave, it was impossible to swim against. Tim Lawrence and Myself had to push and pull ourselves along through the restriction. Each metre of penetration was hard work wriggling through the restrictions and pulling against the current. Fish and rocks came hurtling past, and any sand we disturbed was quickly swept away.
After 20 minutes of struggling against the current we decided to exit, and return the next day at a different state of tide.
On the following day we dived three hours after high tide, hoping that this would be the slackest time to dive. Flow out of the cave
however was not reduced; we managed to lay around 50 metres of new cave line into the cave and must have been close to the exit but again were turned around by the current. We walked over to the lakeward side and quickly located the entrance by following the flow out of the lake.