The Rio de Janeiro Maru has begun leaking oil, raising urgent concerns for environment, tourism, and food security.
OIl leaking from the Rio de Janeiro Maru wreck. Source: Office of the Governor, State of Chuuk
Authorities in Chuuk have confirmed an oil spill from the World War II wreck of the Rio de Janeiro Maru in Uman, Chuuk Lagoon. The leak, first noticed by divers on 11 September and confirmed on 13 September 2025, has released oil near one of the lagoon’s most popular wrecks. Officials warn the incident highlights the wider risk posed by the 63 wartime wrecks scattered across the lagoon.
The incident
Divers aboard the tourist vessel Odyssey witnessed oil surfacing around the wreck, which lies off Uman. The Rio de Janeiro Maru, an 80-year-old Japanese passenger-cargo vessel sunk during fighting with the United States in 1944, is believed to have ruptured a fuel tank. Initial assessments suggest the Southern Namoneas area, particularly Uman Fonuweisom, will be most affected.
Response efforts
Local authorities—including the Division of EPA, Chuuk Public Safety, and the Disaster Office—are coordinating an immediate response while assessing environmental and food security risks. The Japanese company JMAS has previously conducted small-scale oil removal in Chuuk, but large-scale containment and recovery may require international support. The Chuuk Government has requested assistance and recognition of the spill from U.S. agencies and other partners.
Wider risks
The lagoon’s shipwrecks, many still containing oil and other hazardous materials, are deteriorating under the combined pressures of corrosion and climate change. Conservation groups have long warned that a major leak was inevitable without proactive action. A Chuuk government spokesperson described the spill as “a warning that we must act decisively to protect our environment, food security, and the well-being of our people.”
Expert voices
Pete Mesley of Lust4Rust, a long-time business associate and occasional contributor to X-Ray Mag, reflected on the incident: “And so it begins. As predicted by many. One of the wrecks in Chuuk have split one of their fuel tanks… Hopefully now progress will be sped up to further reduce the devastation the leaking oil will have not only on tourism but also on the livelihoods of the local people.”
Fact file
The Rio de Janeiro Maru was built in 1930 by Mitsubishi Shipbuilding & Engineering in Nagasaki for the Osaka Shosen Kaisha Line as a passenger-cargo liner. Around 1940, it was requisitioned by the Japanese government and served first as a submarine tender and later as a transport vessel during the Second World War.
During Operation Hailstone in February 1944, while anchored east of Uman Island in Chuuk Lagoon, the ship came under heavy attack from U.S. carrier aircraft and sank shortly after midnight. Measuring about 141 metres in length and displacing roughly 9,600 tons, the vessel was among the larger wartime wrecks in the lagoon.
Today, the wreck lies on its starboard side in about 34 to 35 metres of water. Much of its structure remains intact, including the stern and bow guns, cargo holds, and engine room. Artefacts such as crates and bottles are still visible, and the wreck is heavily encrusted with corals and sponges, making it both an important historic site and a notable dive attraction.
