A well-known environmental research vessel sank Sunday evening while docked in the Oakland Estuary. No one was onboard, and firefighters worked to contain the nearly 400 gallons of diesel that was onboard.

As the Chronicle reports, the Kaisei, a large double-masted replica ship operated by the Ocean Voyages Institute in Sausalito, began sinking around 6 p.m. near the 2500 block of Blanding Avenue in Alameda. Witnesses on land saw the vessel partially submerged and alerted authorities, according to US Coast Guard spokesperson Petty Officer Kenneth Wiese.

Via Alameda City Fire Department

Crews from both Alameda and Oakland fire departments responded, including a fireboat, and worked to stabilize the scene. As NBC Bay Area reports, the ship had begun pulling part of the dock down with it, and responders cut the mooring lines to prevent further structural damage, according to Alameda Fire Department Public Information Officer Kevin Tidwell.

The Kaisei, which was not occupied at the time of the incident, has since settled on the estuary floor. Firefighters deployed a floating boom around the wreck to contain a visible sheen of leaking fuel, as reported by ABC7. The vessel is believed to have contained up to 400 gallons of diesel onboard, Wiese said.

Via Alameda City Fire Department

A person reached at a number associated with the Kaisei Project told theSan Francisco Chronicle they believed “something hit” the vessel, though the exact cause of the sinking remains under investigation. Officials with the Coast Guard and other agencies are monitoring the situation and coordinating next steps, which could involve salvage or removal depending on the assessment of the ship’s condition.

The Kaisei is a modern replica of a traditional Japanese training vessel and serves as the flagship for the Ocean Voyages Institute’s cleanup missions. The nonprofit has operated out of Sausalito since 1979 and launched the Kaisei Project to remove plastic waste and marine debris from the Pacific, including three expeditions to the North Pacific Garbage Patch.

The ship at full sail via Ocean Voyages Institute

Based on a Reddit post from five years ago, it appears that the Kaisei was routinely docked in Alameda between expeditions:

The Kaisei currently docked in Alameda. The brigantine is currently operated by Ocean Voyages Institute as the figurehead and expedition ship of "Project Kaisei" which is an international program dedicated to implementing solutions to the problem of marine debris.
byu/carnegiehall insailing

The ship’s sinking has raised concern among environmental advocates, given its symbolic role in ocean preservation. Authorities are urging anyone with information about what may have caused the vessel’s damage to contact the U.S. Coast Guard.

Top image via the Ocean Voyages Institute