Overview of Osezaki

The long, narrow cape in the middle is part of Osezaki. It is nestled in the embrace of Mount Fuji and faces Suruga Bay, making it an ideal diving area.

Osezaki is located in eastern Shizuoka Prefecture, at the western foot of the Izu Peninsula, which was once an island but was connected to Honshu due to tectonic movements. It is a legendary diving area that was opened in the early 1980s with the cooperation of the fishermen's union, following in the footsteps of Izu Marine Park on the east side of the Izu Peninsula.

Facing Suruga Bay, the deepest bay in Japan with a maximum depth of 2,500m, the area is known for its rich biodiversity, with deep-sea creatures appearing and divers delighted with megafauna such as whales, manta rays and ocean sunfish, while also being home to tiny sea slugs, frogfish and gobies that are the envy of photo-obsessed divers.

The dive sites are roughly divided into the "inner bay" which is an inland sea along the curvature of the cape, and several spots in the "outer sea" which has been developed on the outside.

Diving Basic Information

Beach diving is the norm at Osezaki

A beach that stretches out facing the inner bay of Osezaki. It also becomes a popular swimming spot in the summer.
Photo by Nature Inn Osekan

Beach diving and boat diving are available at Osezaki. Many divers dive in both the inland and open seas when beach diving, but the "inner bay" is particularly popular. Because the "inner bay" is easy to enter and exit, the sea is calm most of the year, and there is plenty to see.
You can walk to the dive sites in the open sea, but since it's difficult to carry your equipment on your back, it's common to load your equipment onto a cart that can be rented from the diving centers at Osezaki and head to the spot. Alternatively, you can get to the dive sites by boat from the pier on the right side of the bay. It's only about a 10-minute trip each way.

Local guides will show you around the underwater world.

There is also a chance to see the rare hatching of the yellow pygmy-goby eggs, a popular fish in the bay.
Photo by Kumiko Maki (Nature Inn Osekan)

Self-diving is permitted at Osezaki, provided that two or more have experience of the waters of Osezaki, or that at least one professional-level C-card holder is present. There are diving shop tours in Numazu, Mishima and other areas where instructors accompany you, there are many divers who visit Osezaki on diving shop tours.
If you are diving at Osezaki on your own, we recommend signing up for a guided dive using Osezaki's diving centers. Local guides guide almost every day, and even when there are no guests, they dive and explore, so they know every inch of the underwater world, making diving an exceptionally enjoyable experience.

A Day of Diving in Osezaki

Beach diving is the norm at Osezaki, and entry times vary depending on the group. There are usually two to three dives per day, so depending on arrival times, you'll probably do one or two dives in the morning and one or two in the afternoon.

You will need to use the changing rooms and lounges within the diving center to change clothes and eat. You may purchase lunch at a convenience store along the way, but some diving centers also provide meals.

Boat dive sites at Osezaki

You can also enjoy the fantastic underwater scenery at the "Hotoke Rock."
Photo by Shincho Yoshida (COCOMO OSEZAKI)

Although Osezaki is popular for beach diving, there are also dive sites accessible by boat. Perhaps because there are hardly any divers, the untouched waters are characterized by a lush soft coral and wild nature. There are only a few diving centers that offer boat diving, so be sure to check in advance and apply.

Seasonality

Osezaki is located deep in Suruga Bay, and is hardly affected by weather or sea conditions, so you can dive there all year round. We will introduce the water temperature, sea conditions, and highlights for each season.

【Spring】

From the end of March to early July, the water temperature is 16-18°C. The wind direction is variable, with northwesterly and southwesterly winds blowing alternately. The northwesterly wind can make the open sea a little rough. A dry suit, a two-piece suit with a hood and a thickness of 5-6.6 mm or more, is recommended.
In the spring, you can see various young fish attached to the seaweed called Gulfweed in the ocean, and the mouth-rearing of cardinalfish is also a highlight.

【Summer】

From late June to early October, the water temperature is around 18-24°C (it has tended to be a little warmer in recent years). In addition to southwesterly winds, there are also northeasterly winds, so Osezaki is hardly affected by the wind. A 5mm one-piece wetsuit is recommended.
In summer, the water temperature rises and the fish population becomes very dense. Seasonal migratory fish from the southern seas also begin to appear.

【Autumn】

From the end of September to December, the water temperature is around 26°C at its highest and around 18°C at its lowest. In addition to northeasterly winds, westerly winds often blow, and when there is a northeasterly wind, diving on the eastern side of Izu becomes impossible, and divers concentrate in western Izu, such as at Cape Osezaki. Wetsuits are 5mm one-piece or two-piece. Drysuits are also comfortable as long as you wear a thin inner layer.
Migratory fish such as yellowtail and amberjack appear. The water is clear and the fish are plentiful, making this the best time of the year.

【Winter】

From January to March, the water temperature at Osezaki is 14-16°C (it has tended to be a little warmer in recent years). The open sea can be a little rough on some days due to westerly to northwesterly winds. A dry suit or a 6.5mm or thicker two-piece suit with a hood is recommended. In winter, you can see anglerfish and John Dory coming up from the depths of the ocean. The number of sea slugs also increases, and you may encounter dozens of different species on a single dive!

Dive sites information

Inner bay

Wannai

Angler fish that is often requested by divers from overseas to see.　
Photo by Mikiya Wakamatsu (Nature Inn Osekan)

"The bay area (Wannnai) of Osezaki is a world class beach dive," says Maki (mentioned above). "The most attractive thing about the bay is the stability. Osezaki is a beach entry, but there are three spots: the bay, the open sea, and the tip. A major advantage of the bay is that it is rarely closed unless there is a typhoon or other major event.
Guide ropes are strung underwater, making it easy to follow, and it's a great place to try self-diving with a buddy. It's also fun to take photos after checking the ocean conditions and wildlife information at each service. Why not try your hand at winning the Osezaki Calendar Photo Contest, held every year?

In spring, you can see the adorable sight of small frogfish and Pikachu nudibranch perched on tree-like bryozoans sp.. You can choose the background color to photograph, such as the yellow to green seaweed or the red algae.

Summer is the breeding season for many creatures, which means it's the season of love! Even fish that are usually plain will show off stunningly beautiful colors during the moment of courtship. It's difficult to capture that moment in a photo, but the excitement when you manage to capture it as a team effort with your guide is all the more special.

In the summer of 2024, a pier float that allows people to walk on the sea was installed in the bay, and was well received by bathers and divers taking a break.

Ornate ghost pipefish are a popular seasonal migratory fish.
Photo by Kumiko Maki (Nature Inn Osekan)

"The highlights of autumn are the seasonal migratory fish and their schools. There are also an increasing number of gobies, the skillfully camouflaged Robust ghost pipefish, the colorful Ornate ghost pipefish, South-Pacific sergeant, and the small Black rayed shrimp-goby. The land temperature is comfortable and the water temperature is still warm, making it a great season for just diving. "

"Winter, when Mount Fuji is covered in snow, is actually Cape Osezaki's hidden best season. The seawater is crisp and clear, and you might encounter young deep-sea fish such as anglerfish that have come up from the depths or oarfish carried by the seasonal winds. Both the land and sea are less crowded than in summer, so you can relax and enjoy the day, which is great."

Open sea

Misaki no Sentan (The tip of a cape)

At open Sea, The tip of the cape
Video provided by Kumiko Maki (Nature Inn Osekan)

The tip of the cape that separates the bay from the open sea is a special dive site that is only open on weekends and holidays.
"The tip, a limited-time only available on weekends and holidays, is located within the grounds of Ose Shrine. You push a cart through the torii gate, bow to Ose Shrine and head to the tip. As you enter the water, you feel even closer to Mount Fuji than you would in the bay, and the blue of the Neon damsel (fish) and the orange of the Scalefin anthias welcome you like a shower of cherry blossom petals," says Maki (as mentioned above).

The blue sea is filled with well-grown soft coral. Wrasses also flock to them.
Photo by Kumiko Maki (Nature Inn Osekan)

"In the summer, it's fun to watch the mating behavior of wrasses. You can observe a variety of wrasses, such as the Chinese wrasse and the Moon wrasse, spreading their fins to court each other. If you're lucky, you might even see a hammerhead shark!
In autumn, anthias become active in schools and the seasonal migratory fish, the Fire goby, appears. Schools of mullet, grunt and damselfish also grow larger. Large schools of mullet fill the field of view like a wall.

Winter also sees much better visibility, making it the perfect season for wide-angle photography of anthias schooling around soft corals. It feels so luxurious to be able to enter the water while looking out at the snow-capped Mount Fuji. "

A weedy scorpionfish found at the "tip" of the river.
Photo by Yoshihiro Shincho (COCOMO OSEZAKI)

Many guides at Cape Osezaki prefer the "tip," and Yoshihiro Arata of COCOMO OSEZAKI gives it high praise.
"From spring to summer, the number of juvenile blue damselfish and goldfish anthias begins to increase, making the sea very lively. Whale sharks and manta rays have been seen here, so it's an exciting time when you never know what you'll see.
Autumn is the best season to observe many species of fish, but in recent years, the most popular are schools of Fire goby and Purple Fire Goby, some rare damselfish and anthias, making it a time when you can encounter a variety of rare creatures and never run out of subjects to photograph.
In winter, when the water temperature drops, many sea slugs and deep-sea creatures can be seen. I have also seen Anglerfish."

Sakushita (Under the fence）

Ortmann's spider-crab（Chirostylus ortmanni）is not a shrimp,but a relative of hermit crabs.　
Photo by Marine Photo Library

This is the northernmost of the open sea dive sites, and as it is close to the "tip," the gently sloping drop-off is home to a colony of whip coral, and schools of fish such as half-lined cardinalfish, one-striped anthias and cherry anthias.

Monshita

Juvenile pinecone fish（Monocentris japonica）found in Monshita.
Photo by Marine Photo Library

The entry point is just before the open sea road ends. In the shallows, you can see popular subjects for photographers, and there are also interesting places with crevasses and caves.

Ipponmatsu

At Cape Osezaki, the chances of encountering ocean sunfish increase in early spring.
Photo by Yoshihiro Shincho (COCOMO OSEZAKI)

The spot was named when there was only one pine tree growing along the coastline. The seabed changes from gravel to a vast expanse of sand. According to Shincho (mentioned above), "In spring, the shallow waters are covered with a seaweed called Kagikenori, staining the bottom pink. This is also the time when large schools of mullet can be seen, and the area is bustling with divers looking to catch ocean sunfish."
From summer to autumn, many popular species such as the frogfish and ghost pipefish can be seen, making for a gorgeous backdrop for macro photography. Many species of damselfish and frogfish can be observed on the shoreline.　 Winter is sea slug season. You can observe many different kinds of sea slugs, and it may not be difficult to see over 30 species in one dive."

Hotokeiwa

The spikes on Hotoke Rock are wild and huge!
Photo by Yoshihiro Shincho (COCOMO OSEZAKI)

COCOMO OSEZAKI actively recommends boat diving. When we asked Shincho about the highlights of Hotokeiwa, he said, "It's the dive site at Osezaki that's best suited to wide-angle photography, and it's interesting to observe the creatures, so you can also take macro shots. There are often currents, but that means you can encounter a wide variety of creatures."

Eagle rays can be seen in large numbers around Hotoke Rock from spring to summer, and from early summer several eagle rays can be seen circling Hotoke Rock. This is also the time when sightings of hammerheads increase.

From summer to autumn, you can observe amberjacks attacking schools of yellowtail and grunt. Recently, there is a good chance of encountering sea turtles. This is also the time when many seasonal migratory fish can be seen, including damselfish, butterflyfish, angelfish, and gobies in the sandy areas.

You can also see the popular sea slug nicknamed Pikachu.

Visibility increases from autumn to winter, making it a good time to take wide-angle shots of soft corals. There are also many sea slugs, and you have a good chance of encountering popular species such as Pikachu.

Shiragake

We asked Shincho about the highlights of the boat spot "Shiragake."
"Compared to Hotoke Rock, the current is gentler and it's suitable for beginners to intermediate level divers. The bottom of the water is a gentle rocky slope, and if you go down there you'll find a wide expanse of sand.　
From spring to summer, the number of juvenile fish increases, and in areas where sea anemones grow in large numbers, you can observe clownfish eggs and juveniles, and from summer to autumn, you can observe ghost pipefish and juvenile spotted thrush, and the chances of encountering sea turtles also increase significantly. In winter, the waters are a little deeper, but you can also observe sea slugs such as the horned sea slug and the cannula horned sea slug in the sandy areas.

Diving shop

nature Inn OSEKAN

divebookings@natureinn.jp

DIVE HOUSE OSPER

ose@osper.co.jp

Marin House Lei aloha

osezaki@leialoha.join-us.jp

*Please note that not all diving shops on the list have English speaking staff.
*Please choose the diving shops at your own risk. We’re not responsible for any accidents / troubles.

A Day of Diving in Osezaki

On a clear day, you can enjoy diving at Osezaki while looking at Mt. Fuji.

Beach diving is the norm at Osezaki, and entry times vary depending on the group. There are usually two to three dives per day, so depending on arrival times, you'll probably do one or two dives in the morning and one or two in the afternoon.

Diving shop tours also use the local seaside diving centers, but you will set up your diving equipment on a plastic sheet laid out on the beach in front of you. Each group is separated, so be careful not to mix up your equipment. You will need to use the changing rooms and lounges within the diving center to change clothes and eat. You may purchase lunch at a convenience store along the way, but some diving centers also provide meals.

Travel Information

Access to Osezaki

By Train

The nearest stations to Osezaki are JR Mishima Station, which is about 40 to 55 minutes away from Tokyo on the Tokaido Shinkansen, JR Numazu Station on the Tokaido Line, and Izunagaoka Station on the Izu Hakone Railway Sunzu Line.
There are two round-trip buses per day to Osezaki from the south exit of Numazu Station, and several buses to nearby Enashi Station each day. The diving center you use can also provide transportation from each station during certain hours, so it's a good idea to inquire. It takes just over an hour to get to Osezaki from Numazu Station by bus. In the summer, there is a regular ferry service to Osezaki that takes 30 minutes from Numazu Port, which is about a 10-minute bus ride from Numazu Station.

By Car

From either the Kanto or Nagoya area, take the Tomei Expressway or Shin-Tomei Expressway and exit at Nagaizumi-Numazu IC. Then, take the Higashi-Suruga Ring Road (Izu Jukan Expressway), National Route 136 (Izu Chuo Expressway) to Izu-Nagaoka IC. Continue along the road towards Osezaki. If everything goes smoothly, it takes about an hour to get from Nagaizumi-Numazu IC to Osezaki. On the way back, it may take longer due to traffic congestion.

Internet

Free Wi-Fi available at the dive shop

Payment

Many accommodations and dive centers also accept credit cards, but we recommend checking in advance.

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