Ogasawara Dive Sites & Marine Life

If the main Ogasawara guide sold you on the idea of diving Japan's mid-Pacific outpost, this page is the dive plan. The Bonins are a volcanic archipelago around 1,000 km south of Tokyo, and their underwater character is all drama: lava terrain riddled with arches, holes and pinnacles, water that drops away into deep blue, and pelagic life that shows up in numbers you rarely see elsewhere in Japanese waters. Below are the signature sites, what swims there, and how to handle the journey to reach them.

Maguro-ana: the Tuna Hole

The site every Ogasawara diver wants is Maguro-ana — literally "Tuna Hole." It's a great open archway in the lava, roughly 20 metres wide and dropping toward 50 metres, with the swim-through itself sitting at a comfortable 10 metres or so. The reason for the name circles overhead: in summer and autumn the arch fills with dogtooth tuna, sometimes a hundred or more, the biggest pushing two metres. They hang in the current like a slow silver carousel, utterly indifferent to divers below. Currents here can run hard, so it suits intermediate and advanced divers more than fresh C-card holders.

Hang back near the lava and let the tuna come to you. Chasing a fast pelagic only burns air and scatters the school — patience is what turns a glimpse into a swarm.

Sharks: where and when

Ogasawara has become one of Japan's most reliable spots for predictable shark encounters. Sand tiger sharks (ragged-tooth) aggregate in the islands' shallows, and since recent years dedicated trips off Chichijima and nearby islets run mainly from November to February, when small groups gather and recreational divers can watch them cruise the rocky shallows. Their snaggle-toothed grin looks fearsome but their temperament is calm. Beyond the sand tigers, grey reef and other requiem sharks patrol the deeper drop-offs and the cave-and-hole sites scattered around the outer islands.

Beyond Chichijima: Hahajima and the outer islands

Most visitors base themselves on Chichijima, but the diving widens considerably if you push further. Hahajima, a two-hour ferry hop south, sits at the centre of five distinct dive zones: dramatic seascapes to the south, sandy slopes to the north, coral gardens to the east, and rugged pelagic terrain to the west. Offshore, North-West Otouto-jima hides submerged caverns around 22 metres, and the Hahajima West Pinnacle breaks the surface as exposed rock before plunging into crevasses past 30 metres. Northward toward the Mukojima and Hirashima groups, the cast changes again — this is dolphin and whale water, and a string of "shark cave" and "tuna cave" sites reward divers willing to make the longer boat run.

The supporting cast

• Dolphins — bottlenose and spinner dolphins are present year-round and frequently met on the surface or while snorkelling between dives.
• Fusiliers — clouds of blue-and-yellow and bartail fusiliers drape the reefs and add living colour to the black lava.
• Sea turtles — green turtles are a familiar sight; Ogasawara is one of their important nesting regions.
• Humpback whales — from winter into spring (roughly February to April) they pass through, often heard underwater long before seen.

Reading the underwater terrain

Ogasawara is volcanic to its core, and the topography is half the appeal. Expect lava ridges, sheer walls, swim-through arches, pinnacles rising from deep water, and caverns where light shafts down through gaps in the rock. Because the islands sit far out in clean ocean, visibility regularly runs 15 to 40 metres, with the clearest water in the calm summer stretch. There's little run-off and no big-city silt — just blue water over black rock and the occasional pale sand patch.

Plan your dive

• Best season: Diving is year-round, but June to September brings the warmest water, calmest seas and best visibility — and the peak of the Maguro-ana tuna action. For sand tiger sharks, aim November to February; for humpbacks, late winter into spring.
• Water temperature: Around 27–29°C in summer, easing to 21–23°C in the coolest winter months, with 24–26°C in spring and autumn. A 3mm suit suits summer; bring more neoprene for winter shark trips.
• Visibility: Typically 15–40 metres, best from June to September.
• Level: Plenty of gentle reef diving for newer divers, but the marquee sites — Maguro-ana, outer pinnacles and cave systems — involve current and depth. Build a few dives early in the trip before tackling them.
• Getting there: There is no airport. The Ogasawara Maru sails from Takeshiba Pier in Tokyo and takes about 24 hours to Chichijima, running roughly every three days in busy periods and less often in low season. Because the ship usually stays in port a few days before returning, a typical trip runs about five to six days — lock in your dates, then build everything around the sailing schedule.

Tips for the long ferry crossing

• Book the ferry and your accommodation together and early; sailings are infrequent and berths fill in summer.
• Pack seasickness remedies — the open-ocean leg can get lively. A reserved bunk or cabin makes the overnight passage far more bearable.
• Bring everything you'll need; resupply on a remote island is limited, so carry your own essentials, save-a-dive spares and any specialist gear.
• Plan a rest day on arrival before your first dive to shake off the crossing and check conditions with local operators.

Ready to map the wider region? See where Ogasawara sits among Japan's dive areas on our dive maps, and revisit the main Ogasawara guide for the big-picture overview of these remarkable islands.