Katsuura & Namegawa · Japan · Pinnacle · Reef · Pelagic & blue water
Isomura
Houndsharks resting in a cave at the tip of the south reef
Isomura is the huge offshore pinnacle that stands for Katsuura diving, a mass of rock ringed by white sand and too large to circle in a single dive. Current reaches it and fish gather thickly, so the attraction is schools of grunt and passing amberjack around a reef cut with crevasses, shelves and a cave where sharks rest.
Also known as イソムラ.
Where it is and how deep
No published position for this site — the map shows Katsuura & Namegawa and its other sites; operators know the mooring.
The dive
The pinnacle rises from a floor of white sand and is split by several large crevasses. The central crevasse sometimes fills with grunt, and bullhead sharks tuck into the shelves, so a torch is needed to look into them.
At the tip of the south reef, at 30 m, a horizontal hole runs into the rock, and banded houndsharks often lie resting inside it. Out over the reef, schools of grunt and takabe hang in the water while amberjack and greater amberjack circle past; a big yellowtail amberjack shows up now and then, and conger eels and longtooth grouper live on the rock.
Marine life and season
- Reef fish swarms
- Trevally & jacks
- Groupers
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Prime | Prime | Prime | Good | Good | Good | Good | Good | Good | Good | Good | Prime |
Season follows Katsuura & Namegawa: Diving runs all year; winter opens Umanose and brings lumpfish onto the sand, in the coldest water of the year.
Know before you go
- Current runs over the pinnacle, the same flow that brings in its schools of fish and passing amberjack.
Questions divers ask
What certification does Isomura need?+
Advanced Open Water. The shark cave at the tip of the south reef lies at 30 m, and the offshore boat points take certified divers only.
Sources
- Isomura (Katsuura Diving Service) — 勝浦ダイビングサービス
- 勝浦blueの海でダイビング — Katsuura City Tourism Association
More dive sites in Katsuura & Namegawa
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
Similar dives elsewhere
Pinnacle
Ootaka-ne
Miura Peninsula · Japan
Soft corals blanketing the walls of the northern drop-off
A current-swept pinnacle from 30 m to within 5 m of the surface
Three rock heads with table coral, 5 m down to 30 m
The sec du Pelu, renamed for the groupers that hold on it