East Asia · Japan
Katsuura & Namegawa
Kuroshio-fed pinnacles with amberjack schools within reach of Tokyo
Katsuura sits midway down the Pacific side of the Boso Peninsula, where the Kuroshio and Oyashio currents meet and keep the rocky reefs thick with fish. Boats from Uhara run out to Isomura, a huge pinnacle ringed by white sand and cut with crevasses, and Umanose, open only in winter, has the best odds of big pelagics. Benten draws macro hunters, Shimura Beach suits newer divers from shore, and Namegawa adds a shallow point a minute from its harbour.
About diving in Katsuura & Namegawa
Katsuura's diving splits between Uhara and Namegawa. At Uhara, Shimura Beach is entered from the fishing co-op's fish-pen facility, with guide ropes, buoys and a 30 m line laid for training. Boats reach Uhara-jima in about three minutes and the giant pinnacle of Isomura in a short run further offshore. At Namegawa a small outboard boat takes divers to the shallow inshore point in a minute, which suits anyone prone to seasickness.
The seabed is a landscape of rock pinnacles rising from white sand. Isomura is too large to circle in one dive, with a tall drop from its top to the sand and several big crevasses. Uhara-jima's rock walls run from 5 to 25 m, and Benten is open sand with scattered rocks, gentle enough for a relaxed dive. Where the Kuroshio meets the Oyashio the water is rich: schools of grunt and takabe, greater amberjack, yellowtail and sometimes big yellowtail amberjack, with bullhead sharks, conger eels and longtooth grouper at Isomura.
Newer divers have plenty: the shore site, Benten and Uhara-jima all take beginners, and Namegawa's inshore point stays shallow and hosts try-dives and courses. Even on a try-dive or snorkel, colourful tropical fish such as clownfish and butterflyfish turn up. Divers after big fish should come in winter and be ready for current; Umanose is an advanced site to 40 m.
Best time to dive Katsuura & Namegawa
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Prime | Prime | Prime | Good | Good | Good | Good | Good | Good | Good | Good | Prime |
The Uhara shop runs courses and fun dives all year. Winter is when Umanose opens, an area the fishermen work for the rest of the year, and lumpfish start to appear on Benten's sand; at Namegawa they arrive in numbers in spring. The sea is coldest in February and March at about 17 °C and warmest in August and September at about 26 °C.
Dive types & marine life
Schools of grunt and takabe and passing amberjack are the draw at Isomura, with yellowtail amberjack an occasional bonus. Big pelagics are likeliest at Umanose, which opens only in winter. Lumpfish appear on Benten from winter and gather in numbers at Namegawa in spring.
- Reef
- Muck & macro
- Pelagic & blue water
- Trevally & jacks
- Reef fish swarms
- Groupers
- Frogfish
- Nudibranchs
- Macro critters
Best dive sites in Katsuura & Namegawa
- 1
Isomura
Katsuura's signature pinnacle, ringed by white sand and cut by crevasses, with amberjack and grouper.
- 2
Umanose
Advanced point to 40 m in strong current, with very dense fish life.
- 3
Uhara-jima
Island three minutes from port, sheltered from south winds, with rock walls from 5 to 25 m.
- 4
Benten
White sand with scattered rocks and little current; seahorses, frogfish and winter lumpfish.
- 5
Shimura Beach
Wide shore site west of the Katsuura marine park tower, with roped training lines.
Site guides
Pinnacle
Houndsharks resting in a cave at the tip of the south reef
Reef
A one-minute boat ride to a shallow rocky site
Wall
A maze of ledges where bullhead sharks rest
Reef
Amberjack schools over a winter-only fishing ground
How to get to Katsuura & Namegawa
Katsuura lies 70 to 80 km from central Tokyo. Wakashio express trains from Tokyo Station stop at Katsuura, and highway buses from the Yaesu side of Tokyo Station run through the Aqua Line tunnel. Drivers to Namegawa leave the expressway at Ichihara-Tsurumai and follow Route 297.
Photos from Katsuura & Namegawa
くろふね · CC BY 3.0
663highland · CC BY-SA 4.0
Questions divers ask
Can beginners dive at Katsuura?+
Yes. Shimura Beach has guide ropes, buoys and a 30 m training line, Benten has little current, and Uhara-jima is sheltered from south winds. The offshore boat points take certified divers only.
When can Umanose be dived?+
Only in winter. Fishermen use the area for the rest of the year. It reaches 40 m with strong current, so it is an advanced dive.
Which site suits macro photography?+
Benten, for seahorses, frogfish, nudibranchs and lumpfish from winter. Namegawa's inshore point is shallow throughout, so photographers can take their time there.
What certification do the deeper Katsuura sites need?+
Isomura reaches about 30 m, the limit an Advanced Open Water course qualifies divers for, and Umanose goes to 40 m.
Sources
- KDS about — Katsuura Diving Service
- KDS dive points — Katsuura Diving Service
- KDS home — Katsuura Diving Service
- Namegawa Diving Service — Namegawa Diving Service
- Diving in Katsuura — Katsuura City Tourism Association
- Katsuura, Chiba — Wikipedia
- Onjuku — Wikivoyage
- Katsuura average sea temperatures — SeaTemperature.org
Photo credits
- A calm inlet with fishing boats moored at a harbour wall, framed by wooded sandstone cliffs under a clear sky by くろふね, CC BY 3.0, via Wikimedia Commons
- Waves rolling onto a sandy beach below pale layered sandstone cliffs topped with green trees, a few surfers in the water by 663highland, CC BY-SA 4.0, via Wikimedia Commons
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