Safety · Destination Guide
Boso Peninsula
From Tateyama shark encounters to Katsuura macro reefs, just beyond Tokyo.
Safety · Destination Guide
From Tateyama shark encounters to Katsuura macro reefs, just beyond Tokyo.
Treat this as a temperate, operating-cooperative-managed and sometimes high-current coast. Verify local guide permissions and evacuations before booking. Ito involves close animals and potential lost-mask or regulator events; outer reefs may have strong water movement; supervised bathing zones and dangerous coasts must be distinguished. For emergencies call 119 (ambulance) or 118 (sea rescue), not the dive shop alone.
At Ito, use only the qualified operator boat excursion: BOMMIE requires AOW, 30 logged dives, a dive within one year, boat experience and calm mask/regulator recovery. It warns of currents at the surface and descent rope, especially July-October. Do not touch or feed sharks and rays; controlled feeding is done by staff. For Namegawa Maguro-ne and Katsuura boat reefs, request a site-specific current and depth briefing. Cavern-like overhangs and wrecks do not confer overhead-entry privileges.
Tateyama City explicitly lists Okinoshima north/west, Heisura and Mera as dangerous swimming zones. Shallow water can still have fast drift. Snorkel only with appropriate support, in approved sections, and do not use the Ito fishing/boat site as a snorkel entry. Breath-hold training requires rescue-capable buddy/instructor observation and no solo attempts. Check JMA storm and tsunami warnings and local evacuation notices.
For acute injury or suspected decompression illness, call 119 first, or 118 if a maritime rescue is needed. Administer appropriate emergency first aid including oxygen if trained and equipment is available, and follow emergency medical instructions. DAN Japan has a member emergency advice line but is not a substitute for dispatch. Chiba Prefecture lists emergency hospitals including Shioda Hospital in Katsuura and Awa-area centers. No exact recompression chamber, chamber operating hours, travel-time or emergency-transport guarantee was independently verified for this research. Confirm operator oxygen provision, boat communication, nearest accepting hospital and recompression pathway before technical or multi-day dives.
Strong Ito entry current
BOMMIE reports occasional flow too strong to fin against, necessitating drift-line and descent-rope discipline. Its English booking rules specify AOW, 30 logged dives and recent boat experience.
Explicitly hazardous Tateyama swimming areas
City guidance warns against swimming or independent snorkeling off Okinoshima north/west, Heisura and Mera. An August 2025 Okinoshima north-side snorkel drowning is cited by the city.
Storm season, swells and poor visibility
JMA notes elevated typhoon approach risk July-October. Any coast can experience rough seas outside these months; the operator has final authority to cancel.
No unqualified cavern or wreck entry
Kuroiwa overhang and Okinoshima wreck references describe sites, not proof of overhead penetration access or certification waivers.
Ito is a provisioned wildlife dive created in relation to local fixed-net fisheries; guests must not feed, strike, grab or crowd sharks and rays. Follow guide instruction and avoid stressing animals for photographs. Around Okinoshima, Tateyama identifies special protected park vegetation, eelgrass and near-limit coral habitat. Chiba Prefecture prohibits taking specified fishery-rights shellfish and other protected marine animals without authorization, including abalone in prohibited contexts. Do not spear fish, take live shells or collect wildlife, damage corals/sea grasses, litter or trespass in harbors and military-base boundaries. The optional Okinoshima conservation donation does not purchase collection rights.
Do Not Do This
Avoid entering when strong ito entry current. Confirm local briefings before committing.
| Contact | Role | Phone | Availability |
|---|---|---|---|
| Ambulance / Fire (Japan) | Immediate medical response | 119 | 24 hours, every day |
| Japan Coast Guard maritime emergency | Sea rescue or maritime incident | 118 | 24 hours, every day |
| Police (Japan) | Immediate police emergency | 110 | 24 hours, every day |
| DAN Japan emergency hotline | Dive-medicine advice for members after calling emergency responders | +81-3-3812-4999 | 24 hours, every day; member emergency service |
| Chiba emergency medical consultation | Non-life-threatening advice on whether emergency care is needed | #7119 | 24 hours, every day; call 119 immediately for emergencies |
| JNTO Japan Visitor Hotline | Multilingual visitor assistance during incidents | +81-50-3816-2787 | 24 hours, every day; English, Chinese and Korean |