Underwater diving in Guam

Scuba diving tourism is a significant component of the island's tourist activity, in particular for visitors from Japan and South Korea.

Recreational dive sites on Guam include submerged shipwrecks, such as the double wrecks of SMS Cormoran and Tokai Maru, and natural features, such as Blue Hole.

Freedive spearfishing is a culturally and economically important activity for Guam residents, with a history extending to the pre-Spanish CHamoru people.

This was comparable to the second method used by the researchers; using reported daily tank fill numbers, they alternately estimated that there were 256,00 to 340,000 dives annually.

The study used 300,000 as its approximation of the number of dives per year on Guam, with one-third being made by locals and two-thirds by international visitors.

[11] It is the only chamber, also called a dive locker, in the Micronesia region and treats both civilian and military divers suffering from decompression sickness.

The number of divers at Piti Bomb Holes increased dramatically after access to a third location, Outhouse Beach on Apra Harbor, was restricted in 2001.

The threshold at which coral damage can rapidly accumulate is 4,000 to 6,000 dives, putting Piti Bomb Holes at severe risk.

[15] The International Coastal Cleanup is a popular event on Guam, which routinely ranks in the top 25 countries for pounds collected.

[19] A 2017 Western Pacific Regional Fishery Management Council meeting noted that the Marianas Underwater Fishing Federation was taking the lead in teaching spearfishermen to enter their catch in NOAA's Marine Recreational Information Program website/mobile app.

The Federation noted, "they are trying hard to legitimize spearfishing as a sport, [but] there are many others who are pillaging the resources by spearing fish that are too small or taking more than what is needed."

[20] A 2010 study found that the establishment of Guam's marine preserves had more than doubled the death rate by drowning of CHamoru fisherman, including spear fishermen, with the hypothesis being that they were pushed into more hazardous areas.

Prior to the establishment of the preserves in 1997, residents of Guam fished primarily on the western coast, which is leeward of the trade winds, and in the reefs along Cocos Lagoon in the south.

[13] In August 1974, the hulk of RMS Caribia, a decommissioned passenger ship, ran aground at the tip of the Glass Breakwater and broke apart in Typhoon Mary.

The ship salvage to clear the port entrance[35] was complicated by the discovery of a Korean War-era LCU wreck next to Caribia with 50 tons of unexploded ordnance.