Boso Peninsula

The right month depends on the site and your exposure tolerance. BOMMIE reports particularly good Ito visibility in January-March and generally less intense currents between November and June. Water in those months can be cold, so suitable suit and hood choices matter. Katsuura and Namegawa offer other shore and boat diving with more variable seasonal access and visibility. Summer is warmer but Ito currents can be strong and the Japanese typhoon approach season is mainly July-October. Ask the chosen operator about the specific dive site and expected conditions rather than relying on a peninsula-wide best month.

Do not assume they can. Ito Diving Service BOMMIE states on its English page that divers need Advanced Open Water certification, at least 30 logged dives, boat experience and a dive within the previous year. Divers must also recover a regulator and replace a mask calmly and handle potentially strong flow along entry and descent lines. Its Japanese FAQ adds experience deeper than 20 m. Someone without those qualifications should choose an instructor-led program elsewhere, such as a suitable Katsuura introduction, and work toward Ito after gaining verified skills.

The banded houndsharks and red stingrays at Ito are marine animals attracted to an operator-managed feeding site, not an unmanaged pelagic swim. BOMMIE describes using otherwise low-value fish from local fixed-net fisheries and controls how much feed staff deploy. Guests must not independently feed, touch, strike or stress wildlife. The signature experience is guided scuba from a boat and has advanced-diver requirements. No lawful recreational snorkeling-with-sharks product at Ito was verified. Do not approach the fishing boat area independently or interpret a shark photo as public access to the site.

For the Shark Scramble, the correct destination is Ito in Tateyama City, Chiba Prefecture, on the southern Boso Peninsula. A different coastal city called Ito is in Shizuoka Prefecture, near the Izu Peninsula. Tourism sites and mapping searches can conflate them because both render as Ito in English. BOMMIE itself warns international visitors about the two Itos and the separate Tateyamas in Japan. Reserve accommodation and ground transport using the Tateyama, Chiba address, and verify the operator, station and port before departing Tokyo.

Katsuura Diving Service, based around Ubara, advertises instructor-led trial dives and PADI courses. Its trial lesson begins in standing-depth water and moves into a shallow marine area, weather and medical screening permitting. Tateyama also has independent introductory operators, but BOMMIE at Ito explicitly states that its own beginner beach program is suspended and its current shark diving is not beginner instruction. Pick the teaching supplier, age eligibility, language and actual beach before booking. A beginner try dive is not permission to join current-exposed offshore reefs or enter a shipwreck or cavern.

Supervised tours can be offered beyond summer, but that does not make municipal swimming beaches year-round lifeguarded. Tateyama City says its 2026 bathing season ended on August 23; the next year requires its own announcement. Ocean Tateyama advertises guided snorkeling around Saka or Nishikawana beaches, and Katsuura Diving Service has a supervised surface program. Crucially, Tateyama lists the north and west sides of Okinoshima as dangerous swimming zones. Katsuura has public beaches such as Ubara, Moriya and Okitsu, but always check the open zone, warnings and operator before entering.

One locally verified offering is Ocean Tateyama's PADI skin-diver program. Its page describes coaching in equalization, finning and shallow duck dives, with training toward roughly 5 m. That is appropriate to describe as introductory skin diving, not automatically as an AIDA depth course, deep line session or competition-ready training. We did not verify a current dedicated deep-freediving charter or competition schedule in the Tateyama-Katsuura region. Check the instructor qualification, in-water safety cover, site approval, medical requirements and exact course date. Never practice breath holds alone.

Tateyama is reached by the JR Uchibo rail corridor or a Tokyo-area express bus, followed by a local bus, taxi or confirmed dive-shop pickup to the actual launch area. BOMMIE publishes Ito Gyoko bus and some station-transfer guidance, but individual departure times can change. Katsuura is on the JR Sotobo line, with limited-express Wakashio services from Tokyo; local trains serve stations such as Ubara. Gear transport and Namegawa harbor access are additional arrangements. Do not assume a direct transfer between the two dive bases or a passenger boat connection across the peninsula.

No common Boso-wide recreational marine-park tag was verified for the researched operators. That does not mean any shore, harbor or fishing ground is unrestricted. BOMMIE includes local fishing-ground access in the fee for its authorized tours, and the Namegawa cooperative directs guests through local dive guides. Okinoshima has a separate voluntary conservation contribution in its announced summer window, not a scuba permit or shell-collection license. Chiba Prefecture restricts harvesting shellfish and other fishery-rights species. Always confirm the actual site with its managing operator and follow coastal and park rules.

Tateyama offers a practical short outing to Tateyama Castle and Shiroyama Park, the waterfront Nagisa museum, Okinoshima nature walks and an ocean-view onsen at Kyukamura Tateyama. On the Katsuura side, visitors can explore its historic morning market, the Katsuura Undersea Park observation tower and the Ubara coastal walks, with beaches for land-based scenery. These do not require scuba qualifications, but some attractions have closed days and coastal paths can be unsafe during high surf. Arrange shared-vehicle pickups with the diver so that the non-diver is not stranded at an isolated fishery harbor.

Ito operator figures vary substantially, including around 14°C to 16°C in parts of late winter and spring, with summer readings at times reaching 27°C. BOMMIE says a wetsuit of at least 5mm can often work from late May into early November, but recommends a hooded vest except during the warmest stretch. Those recommendations are operator-specific, not guarantees for Katsuura or deeper thermoclines. Divers sensitive to cold should check current logs, discuss drysuit options in advance and confirm gear availability; BOMMIE says it does not offer drysuit rental.

Call 119 for ambulance and fire emergencies, or 118 for rescue at sea. DAN Japan lists an emergency medical consultation line for members at +81-3-3812-4999, but says emergency dispatch takes priority. Chiba Prefecture lists recognized hospitals including Shioda Hospital in Katsuura and facilities in the wider Awa area. This research did not verify a particular hyperbaric chamber, transfer duration or guaranteed intake capacity. Before diving, ask the operator to demonstrate oxygen supply, radio/mobile communication, the nearest accepting emergency unit and how recompression treatment would be coordinated if required.

The researched southern Boso dive circuit is fundamentally land-based. Tokyo visitors regularly reach the region by train, express bus or road and take local guided boat or beach sessions. An overnight stay can make early dives and a weather backup day easier, particularly if trying both Tateyama and Katsuura. No credible currently operating overnight dive vessel serving this exact route was established, so plan accommodation ashore and local dive outings. Keep the two bases distinct, confirm the selected operator's meeting point, and allow time for changing coastal weather. A short boat ride within a dive is not an inter-island sea transfer.