Formed millions of years ago, The Blue Hole is Guam’s most popular and widely visited diving site. It extends down into the reef and is a natural limestone vertical shaft. The diving site is ideal for both advanced divers and new divers.

The entrance of the Blue Hole is located on a broad horizontal rocky shelf, which is around 60 feet below the cliff. The opening of the hole is about 35 X 25 feet. The original depth of the shaft is above 300 feet. The first opening from the shaft to the sea is at 130 feet.

The Blue Hole has unbelievably clear water and this makes the sighting of coral and fish more interesting. Moray eels, sea whips and tropical fishes can be spotted inside the shaft. The shaft also unfolds before the diver a colorful world of soft and hard corals. Some divers have recorded the spotting of the flashlight fish at night.

Around 80 feet above the first opening in the shaft is the reef top and divers can spot large fishes. Eagle rays, dogtooth tuna, trigger fish and large school of fishes can be spotted here. Breathtaking corals and algae are another feature of the reef top.

Snappers, lionfish, rainbow runners and leafish can also be spotted in the region. Occasional sighting of turtles, sharks, dolphins, rays and pilot whales have been reported from the site.

The opening of the shaft is so wide that there is clear light inside the shaft which can misguide the diver regarding depth. Most divers also become unaware of the depth due to the clear water. So divers must closely monitor time and depth. Divers should take safety tubes as the dive site is prone to currents. The water temperature varies from 27 to 29 degree Celsius. The average visibility is 70 feet.

The accessibility to the diving site is through boats. The nearest important town to the Blue Hole is Piti. Guam is under the administration of United States of America so the visa requirements are similar to that of the United States.

There are several commercial dive operators who offer equipments and diving instructions. Guam Tropical Dive Station at Hagatna caters to all the aspects related to diving on the island. Guam Tropical Dive Station sells and rents all equipments related to diving. They also have a repair and maintenance department.

Some of the other places in Guam where you can look out for diving equipments and instructions are Fish Eye Diving Guam Inc and Micronesian Divers Association Inc. at Piti, Blue Ocean Inc. Real World Diving at Hagtana, and Coral Drive and Scuba Company at Tamuning. Pacific Drivers Club of the navy also provides information on diving in the Blue Hole.