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Guam Diving: The Blue Hole, Two Wrecks, Five Preserves
Guam's reputation as a dive island rests on two things: a handful of sites that would be unusual anywhere, and reefs close enough to the shore that much of the underwater island can be reached by walking in. The headline dives are for certified, experienced divers; the island's marine preserves ask only for a mask, fins and some care.
Updated 2026-09-19
The Blue Hole: a shaft through the reef
Toward the tip of Orote Peninsula, a vertical shaft opens in the limestone reef with a wide, heart-shaped mouth, and the water is often clear enough to see its rim from the surface. The shaft drops far deeper than recreational air diving allows, which is why the dive is planned around its window: an opening onto the outer reef wall at about 125 feet (38 metres), where divers leave the shaft after the long descent and ascend along the wall. The depth makes it a dive for advanced, appropriately certified divers only.
Apra Harbor: two world wars on one seabed
Inside Apra Harbor, two ships from two different wars lie side by side. The German cruiser SMS Cormoran was scuttled on her captain's orders during World War I to keep her out of American hands; the Tokai Maru, a Japanese passenger and cargo steamer built in 1930, was torpedoed at anchor in the harbour in January 1943 and sunk by a second submarine attack seven months later. The two hulls rest close enough together for a diver to touch both at once.
The wrecks are deep, and seeing both properly takes at least two dives, so this is again a site for experienced divers with the right training for the depth. Local dive operators run the trips, and they will ask to see certification before taking anyone down.
Five preserves, and the reef from the shore
Guam set aside five marine preserves by local law in 1997 — Tumon Bay, Piti Bomb Holes, Sasa Bay, Achang Reef Flat and Pati Point — covering more than a tenth of its coastline, with fishing restricted inside them. For visitors, that protection is what keeps the shallow reefs lively enough to be worth a snorkel, and the calm lagoon of Tumon Bay is the easiest of them to reach from a hotel.
The Piti Bomb Holes preserve is the best known and most visited. Snorkellers reach it by a sea bridge and steps at Fish Eye Marine Park, where the preserve's protection shows in the sheer number of fish; non-swimmers can watch the same reef from the park's underwater observatory, or walk the seafloor in a helmet-diving session. Wherever you go in, the reef line and its currents set the limits, not the distance from shore.