East Izu

For divers based in Tokyo, the east coast of the Izu Peninsula is the closest thing to a home reef. A string of small fishing harbours and shore-entry coves faces Sagami Bay, each one a short drive off the Izu Skyline and the Tokaido line, and all of them washed by the warm Kuroshio Current sweeping up from the south. The classic plan hasn't changed in decades: leave the city before dawn, be kitting up by mid-morning, fit in two dives and a late lunch, then unwind in a hot spring before the drive home. Volcanic Higashi-Izu sits on the Izu-Tobu volcano field, which is exactly why the coast is lined with both onsen and dramatic lava topography underwater.

What makes the east coast special isn't a single headline site but the variety packed into a 70-kilometre stretch — a soft-coral wall in the morning, a wreck in the afternoon, and on the right summer day tropical strays mixing with cool-water residents over the same rocks.

The signature sites

Izu Ocean Park (IOP)

If east Izu has a flagship, it's Izu Ocean Park, the shore-entry site just south of the Jogasaki cliffs near Ito. A staircase and platform make the entry orderly even when there's swell, and a guide rope leads divers out over a shallow garden of anemones and damselfish before the bottom tilts away. Follow the line one way to the famous underwater post box; follow it the other and the slope becomes a wall draped in pink and purple soft coral, dropping toward sand near 40 metres. There's nearly always action here — stingrays, flounder, moray eels and seasonal schools — which is why it suits both first-timers and seasoned divers logging a tune-up. It's a fitting place to make a first dive after certification.

Futo

A little to the north, Futo is the all-rounder of the coast, with gentle shore entries for beginners and boat sites for the experienced. Its calling card is the bigfin reef squid spawning from roughly June to August, when the animals lay egg clusters on submerged branches in plain view of divers. Autumn brings yellowtail and amberjack, October sees huge schools of mullet pour through, and winter occasionally turns up an ocean sunfish or some odd deep-water visitor.

Hokkawa

Hokkawa is the connoisseur's pick — a small operation that caps daily numbers, so it stays quiet and the reef stays healthy. The terrain is wonderfully complex, with channels and ridges blanketed in soft coral and patrolled by dense clouds of scalefin anthias and chicken grunt. In autumn, lucky divers spot the yuzen (Japanese butterflyfish), a striking black-and-cream species endemic to Japanese waters.

Atami and Ajiro

Atami is the easy one — under an hour from Tokyo by shinkansen — and its draw is a sunken cargo vessel known locally as the chinsen, broken into sections at around 25 to 30 metres and now coated in marine growth. Boats also drop divers onto submerged pinnacles offshore, where you work the steep rock faces. Neighbouring Ajiro is one of the larger working ports on this coast; boats run out to nearby reefs where the regulars include dignified red sea bream cruising past as if they own the place.

Ito, Kawazu, Hokkawa to Shimoda

Ito, a famous hot-spring town, doubles as a base for dynamic boat diving. The pinnacles around Teishi feature arches, caverns and volcanic drop-offs that fall away past 70 metres. Further south, Kawazu is better known for its early cherry blossoms than its reefs, but it offers honest local diving when the swell behaves — and the consolation of an excellent onsen when it doesn't.

At the peninsula's southern tip lies Shimoda, far enough from Tokyo to warrant an overnight. The serious prize here is Mikomoto, a rock island a few kilometres offshore where strong current and big visibility combine to deliver schooling hammerhead sharks through the warm months — an advanced trip that demands experience, fitness and respect for the conditions.

Tropical strays and the seasons

The Kuroshio is the engine behind east Izu's character. Each summer it ferries warm, blue water — and the larvae of tropical reef fish — up from the south. By late summer the rocks host a curious mix: temperate residents alongside angelfish, butterflyfish and other death migrants that arrive on the current but can't survive the cold months. It's a uniquely Japanese phenomenon and a big part of why divers keep coming back.

Plan summer and autumn for warmth, fish action and the best visibility; come in winter for crisp, clear water and the chance of strange deep-water guests.

Plan your dive

• Best season: July to October for the warmest water, tropical strays and clearest visibility; winter (December to February) rewards divers who want sharp clarity and unusual cold-water life.
• Water temperature: roughly 24-27°C in summer and autumn, dropping toward the mid-teens in winter — a 5mm or drysuit setup depending on season.
• Visibility: typically best in late summer and autumn when the Kuroshio is closest; conditions vary site to site and with swell.
• Level: something for everyone — IOP, Futo and many shore coves suit beginners, while Atami's wreck, Ito's pinnacles and Mikomoto's hammerheads are for experienced divers.
• Getting there: the Tokaido line and Izukyu Railway run the length of the coast; Atami is about an hour from Tokyo, and Shimoda is reachable in roughly 2.5 hours on the Odoriko limited express. By car, the Izu Skyline through the Amagi highlands is the scenic route home. See our maps for orientation.

For the wider region — west-coast sites, the Amagi interior and the overall lay of the land — see the main Izu Peninsula guide, or browse all destinations.