Enchanted River

 

The Hinatuan Enchanted River is a complex body of water that can either be a lagoon, a spring, and a river. It is a tidal estuary where its water source is coming from underground on the west during low tide and coming from the east from the Philippine Sea at high tide. This results for the river to be mildly salinated
The lagoon area where it is famous for its blue hue is an opening to an underground cave with a chamber called Mayor's Chamber. The lagoon is 35m (115ft) deep and a narrow passageway beneath its floor connects to an underground cave with its major chamber at 52m (171ft) depth. Beyond the chamber still lies a long and narrow opening descending to about 82m (269ft) in depth. The last expedition to the cave reveals there is still a passageway beneath this depth but is yet to be explored.^[1]

The first exploration to the underground cave of the Hinatuan Enchanted River is made by a group of cave divers led by Dr. Alfonso Amores who perished during its 6th expedition to the cave last June 17, 2014 after failing to exit the narrow entrance to the cave due to a cardiac arrest at 40-meter depth inside the narrow tunnel to the Mayor's Chamber of the underground cave in the Hinatuan Enchanted River.  

http://en.wikipedia.org/wiki/Hinatuan_Enchanted_River