Blue Hole, Natural sinkhole dive site in northern Agat Bay, Guam.
The Blue Hole is a natural sinkhole in Agat Bay that descends vertically through the reef with multiple depth levels for divers to explore. The formation opens at about 18 meters below the surface and continues downward, creating a dramatic underwater passage through limestone and coral structures.
This sinkhole became a notable dive destination as underwater exploration techniques improved in recent decades. Scientific surveys in the early 2000s documented new marine species living within its limestone passages.
Local dive instructors contribute to marine conservation by educating visitors about the protection of the coral reef ecosystem at Blue Hole.
Strong currents run through this area, so divers should watch water conditions and always use a surface marker buoy for safety. Hiring a local guide helps with navigation through the passages and ensures you make the most of your dive time.
The sinkhole features a heart-shaped opening at the surface and a hidden window opening onto the ocean at around 40 meters depth. This window-like feature creates a surprising sight when passing through and makes the dive memorable.
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