JKUEP -Japan Karst & Underwater Exploration Project-

16/08/2026

Kirishima Underwater Cave & Spring Research — July 2026 Collaborative Diving Investigation

From 24 to 26 July 2026, DIVE Explorers conducted a collaborative diving investigation with SPACAEM, a research team led by Specially Appointed Associate Professor Hiroki Manabe (Department of General Education, National Institute of Technology, Sasebo College), at Shimono Dai-2 Doketsu, a cave in Yokogawa, Kirishima City, Kagoshima Prefecture, and at Odemizu Spring nearby.

The dives were carried out by Yosh*taka Isaji and Hirokazu Mori.

Shimono Dai-2 Doketsu was discovered and named by Hiroshi Takashima of Daiichi Institute of Technology. On 26 April 2026, SPACAEM deployed an ROV into the cave's sump and confirmed that a flooded passage may continue beyond it. The ROV footage also captured what was suspected to be a fragment of earthenware on the floor. Our role in this collaboration was the documentation and measurement of the flooded section by divers.

At Odemizu Spring — a spring discharging 22 tonnes of water per minute, long used by the local community — we entered at the vent and descended two metres. At the bottom, water was issuing from the side, but the passage beyond was blocked by rock, with no space for a diver to enter. We therefore moved the investigation to Shimono Dai-2 Doketsu that same afternoon. Establishing that a place cannot be entered is also a result of diving it.

In the flooded section of Shimono Dai-2 Doketsu, we recorded six items: one artefact resembling a vessel fragment, two broken block-shaped pieces of what appears to have been a hearth, one cup-like vessel, and two pieces of wood that appear to have been burnt. None were removed. We limited our work to scaled photography and recording each item's position within the cave. A line was laid to the artefacts so that the same locations can be reached on a return visit. The object suspected in the ROV footage to be a fragment of earthenware was not located during these dives.

The findings were reported to the Kirishima City Board of Education on the evening of 25 July. What these objects are, and from when, is for specialists to determine.

On the same day, we visited Hiroshi Takashima at his laboratory to ask about the hydrogeology of the area. The water in Shimono Dai-2 Doketsu and the water at Odemizu Spring, though they rise from the same ground, are groundwater of different kinds. The visit allowed us to place what we had observed underwater within a geological framework.

Turbidity prevented the planned 3D measurement, which is carried over to the next visit. With the line left in place, we will be able to return to the same locations.

Full report:
https://j-kuep.com/pj-kirishima/

Japanese report:
https://tech-diving.jp/field/field-explore/kirishima

02/08/2026

Exploration of the IJN light cruiser Nagara

On 21 July 2026, a JKUEP team dived the wreck of the Imperial Japanese Navy light cruiser Nagara, which lies on the seabed off Ushibuka, Amakusa City, Kumamoto Prefecture, Japan. The project was conceived and planned by Yosh*taka Isaji, Founder of JKUEP.

Nagara was commissioned in 1922. On 7 August 1944, during the Second World War, she was struck by a torpedo off Ushibuka while on passage from Kagoshima to Sasebo, and sank. Today marks 82 years.

Existing information placed the hull at a depth of around 80 m. The charted depth was also about 80 m.

On the day, however, the echo sounder put the lowest point of the hull at 100 m. The team had not taken the 80 m figure on trust, and had prepared for the deeper case.

Runtime was 162 minutes. Maximum diver depth was 97.9 m.

At the foot of the shot line there was no sign of Nagara. From there, the team ran a search line and began looking for her.

The wreck was found. But the time that could be spent beside the hull was six minutes; the remaining 139 went to decompression.

Only part of the structure could be examined. Within that part, she is sitting upright, deck uppermost, without significant list.

Ropes had been rigged across the deck in her service days, and fishing line and netting are now entangled in them. At this depth, a single mistake breaks the ascent plan. There is no room to move carelessly.

What those six minutes were spent on was photographing, and keeping track of the way back.

Ushibuka holds a memorial service for Nagara every year, and a local museum keeps her history. Documents survive. Testimony survives. What no one had ever seen was the ship herself, on the seabed.

Bereaved family members had asked for a photograph that could be placed before a portrait of the dead. To record, and to return the record to those who are waiting for it — that is what this dive was a process for.

The dive itself is less than twenty percent of an exploration. The other eighty is the boat and her skipper, the surface and mid-water support, the ROV, and the training done beforehand.

▼ Project page
https://j-kuep.com/pj-nagara

▼ Media coverage (The Mainichi)
https://mainichi.jp/english/articles/20260723/p2a/00m/0na/015000c

Team:
Diving Shop Tomikawa (vessel)
Mikimaru (vessel)
Bellport Uto Co., Ltd. (ROV)
Light Studio Co., Ltd. (ROV)
Divers: Yosh*taka Isaji, Yosuke Ogiwara, Hirokazu Mori
Photos: Yosh*taka Isaji

14/07/2026

A new amphipod from the underwater caves of South Daito Island(Minami-Daito Island), Japan

The Japan Karst & Underwater Exploration Project (JKUEP) is glad to share the description of a new amphipod, Bogidiella isajii, from an underwater cave on South Daito Island(Minami-Daito Island) — a small, isolated island in the western Pacific, east of Okinawa.

Only a few millimetres long, translucent, and eyeless, the species lives in the "Black Cave," a flooded limestone cave whose dark, faintly saline (anchialine) water holds the richest cave fauna known on the island. The animals were spotted and collected individually in the water column during cave-diving surveys, and subsequently described by taxonomists. The species name isajii honours Yosh*taka Isaji, who leads JKUEP and discovered and collected the specimens.

Anchialine caves — inland waters with a hidden connection to the sea — are home to some of the most specialised and least-known animals on Earth. Reaching and sampling them demands advanced cave-diving skills; naming the animals they contain demands taxonomic expertise. Bogidiella isajii is a direct result of that partnership between field exploration and science.

The Black Cave holds further animals that remain undescribed. JKUEP will continue to document the karst and underwater environments of Japan, and to bring these hard-to-reach ecosystems within reach of the researchers who study them.

07/07/2026

Exploration of the IJN light cruiser Nagara — Amakusa, Japan

On August 7, 1944, the Imperial Japanese Navy light cruiser Nagara was torpedoed by a US submarine and sank off Ushibuka, Amakusa, in southern Japan. Of her 583 crew, 348 lost their lives.
The sinking was treated as a military secret — yet remembrance in Ushibuka never ceased. Tsuru Sasaki, a local woman who made her living as a traveling vendor, prayed for the crew alone and erected a memorial stone at her own expense. She passed away in 1986; the community has carried her devotion forward, holding a memorial service every year around the anniversary of the sinking.

The wreck rests at a depth of about 80 meters in open water. On one or two days between July 20 and 22, weather permitting, a three-diver team led by underwater explorer Yosh*taka Isaji will document the hull in photographs and video.
No human remains or artifacts will be recovered. The records will be returned to the bereaved families, the Nagara Memorial Museum, and the local community.
If achieved, this is expected to be the first photographic documentation by divers of an Imperial Japanese Navy warship resting in Japanese waters.

The project was announced at a press conference in Amakusa City on July 6, joined by Mr. Seiichiro Nishinaka, grandson of Nagara's captain; Mr. Soichi Fukumoto, former executive director of the Amakusa City Council of Social Welfare and a longtime supporter of the memorial activities; and Mr. Kazumichi Murai of Bellport Uto, who provides ROV support for the exploration.

Updates will follow as the survey proceeds.

Photos: (2) A 1998 newspaper feature on Nagara's final hours. (4) "Inori" (Prayer), a portrait of Tsuru Sasaki, displayed at the Nagara Memorial Museum.

――
旧日本海軍の軽巡洋艦「長良」（熊本県天草市・牛深沖、水深約80m）の潜水調査を、7月20日から22日のうち海況の良い1〜2日間で実施します。

船体を写真と映像で記録し、ご遺族・軍艦長良記念館・地域にお返しします。
遺骨や遺品の収容は行いません。

有人撮影が実現すれば、国内に眠る旧日本海軍の軍艦では初の記録になるとされています。

14/06/2026

【Yosh*taka ISAJI to be featured on “Jounetsu Tairiku”】

Yosh*taka ISAJI, founder of JKUEP, will be featured on “Jounetsu Tairiku,” a nationally broadcast Japanese documentary program by MBS/TBS.

The program will introduce part of his work as an underwater explorer in Japan.

Japan still has many underwater environments that remain difficult to access and not fully documented — submerged caves and underground lakes in karst landscapes, deep shipwrecks, flooded coal mines, and other hard-to-access underwater sites.

Yosh*taka’s work is not only about reaching these places.

It is about entering them with the skills and preparation required, documenting what remains there, and sharing those records with researchers, local communities, media, and related stakeholders.

For JKUEP, this broadcast is an important opportunity for more people in Japan to understand that underwater exploration can also be a form of investigation, documentation, and contribution to science, history, and local memory.

The program is broadcast nationwide in Japan, giving this work an opportunity to reach a much broader audience beyond the diving community.

Broadcast:
MBS/TBS “Jounetsu Tairiku”
Date: June 21th, 2026
Time: 23:00–23:30 JST

Official program page:
https://www.mbs.jp/jounetsu/

Official Individual page:
https://www.mbs.jp/jounetsu/2026/06_21.shtml

More about Yosh*taka ISAJI:
https://tech-diving.jp/profile-en

We will continue sharing updates on Japan’s underwater caves, karst landscapes, shipwrecks, and submerged heritage through JKUEP.

僕が貢献できる場所はどこなのか水中の“未踏”を拓く探検家の生き方

01/06/2026

【Laos Cave Rescue | Search continues for two people still missing】

In Laos, five people who had been confirmed alive inside the cave have been brought out safely.

However, two people are still unaccounted for.

Yesterday, search and assessment work continued on site.

During the operation, a crack was identified in the mountain, which may possibly connect to the cave system below.

There appears to be a space beyond a descent of approximately 100 meters by rope.

Today, a Lao SRT team and additional drainage pumps arrived on site.

SRT — Single Rope Technique — is an essential skill for vertical movement in caves, shafts, and rescue environments.

The team is continuing to assess the crack from the surface side, while also working to drain water from inside the cave.

The situation remains uncertain, and safety must remain the priority for everyone involved.

We continue to hope that the two people who remain missing will be found, and that all rescuers, local teams, and support personnel on site remain safe.

31/05/2026

【Laos Cave Rescue | The rescue operation is still ongoing】
Regarding the two people still missing in the Laotian cave,
it is believed they may be located beyond a flooded, narrow passageway that lies further ahead of the point where the recent rescue took place.

This flooded passageway is extremely narrow,
and it is impossible to pass through without changing one’s posture inside the narrow tunnel.
Visibility is zero due to the murky water.

Due to the significant risks involved, diving will be a last resort.

While attempting to drain the water, we will also try to block the source of the water flowing into the cave from certain sections.

30/05/2026

【Laos Cave Rescue | Five people who had been confirmed alive have been brought out safely】

In Laos, five people who had been confirmed alive inside a flooded cave in an abandoned gold mine have now been brought out safely.

Inside the cave, rescuers had to pass through a long section of extremely narrow passage.

Beyond approximately 200 meters of narrow passage, there was flooded section, with the survivors trapped beyond it.

One person was brought out yesterday by passing through the flooded section with diving equipment, guided by rescue team members.

For the remaining four, the team carried drainage pumps deep into the cave and lowered the water level in the flooded section, allowing them to be brought out.

All five were out of the cave by around 3:00 p.m. local time today. Around 5:00 p.m., heavy rain began in the area.

It was an extremely tight situation.

Yosh*taka Isaji did not end up making a dive during the rescue, as the operation was completed before that became necessary.

Even so, being asked to join this rescue effort as a member of the team was a great honor, and also a serious responsibility.

This experience also reinforced the importance of maintaining strong international relationships among cave diving, exploration, and rescue communities.

There were many lessons and challenges from this operation.

For future situations like this, and for the possibility of cave rescue being needed in Japan, Yosh*taka feels that further preparation is necessary in terms of skills, equipment, coordination, and information sharing.

After returning to Japan, he intends to continue building that preparation.

For now, we are deeply relieved that the five people who had been confirmed alive were able to leave the cave safely.

We are grateful to everyone involved in the rescue and hope for the safety of all those who responded on site.

28/05/2026

【Yosh*taka Isaji will travel to Laos to join the ongoing cave rescue effort】

A rescue operation is currently underway in Laos, where several people have been trapped inside a flooded cave.

According to current reports, five of the seven people have been found alive, while the operation is still continuing.
https://www.bbc.com/news/articles/crkpvxrxgp6o

伊左治 佳孝 of DIVE Explorers / JKUEP will travel to Laos to join the local and international team on site, in response to a recommendation and request from Mikko Paasi and Por Parasu Komaradat, who are already involved in the operation.

Some of the team members currently working at the site, including Mikko and Por, have also supported Yosh*taka’s previous exploration projects in Japan.

However, the focus of this operation is not on us.

The priority is the people waiting to be rescued, and the rescuers, local authorities, and support teams who have already been working on site.

For safety, ethical, and operational reasons, we will not share detailed information about the cave, dive plans, route conditions, or technical procedures at this stage.

Yosh*taka will follow the decisions of the team on site and do what is needed within that structure.

We sincerely hope that all those still inside will be brought out safely as soon as possible.

The search is continuing for a further two villagers who are still missing, rescuers say.

03/05/2026

【Minelayer "Tsubame" project is moving into its next phase】

The investigation of the minelayer Tsubame is now moving toward its next stage.

Based on earlier dives, collected documents, and the review of charted locations, several areas off Miyakojima remain important to re-examine. The next planned step is a sonar survey, allowing us to look at the site from a wider perspective and identify underwater targets more systematically before further direct investigation.

Personally, we don’t feel it’s necessary to insist on diving;
as soon as the sonar identifies a suspicious location, I plan to conduct an investigation using an ROV or underwater drone.
Once we’ve confirmed the presence of a shipwreck, I intend to proceed with the dive.

We will continue preparing carefully and moving forward step by step. Please keep following our work as this project develops further.

坪根 雄大
伊左治 佳孝