A sunken Royal Navy warship in the Baltic Sea is a “ticking timebomb” that could trigger “catastrophic damage” unless urgent action is taken, experts have warned. The Ministry of Defence is preparing a mission to examine HMS Cassandra, a C-Class cruiser that struck a mine and sank just after the end of World War One. She now rests off the Estonian island of Saaremaa, slowly leaking oil. Up to 780 tons of fuel and a stockpile of munitions are thought to remain trapped inside.
The ship is one of an estimated 8,500 wrecks around the world posing serious environmental risks. The MoD’s expedition forms part of a wider push to deal with the threat. The mission is backed by Project Tangaroa, a global campaign highlighting the risk these wrecks pose to marine ecosystems and coastal communities.
Campaign leader Lydia Woolley said: “Potentially polluting wrecks pose a great global threat to coastal communities and marine ecosystems.
“Left unmanaged, they could result in the destruction of vital fishing grounds and coastal tourism. This would have devastating effects on the marine environment, human health and wellbeing, as well as local and regional economies.”
Swedish diver Marcus Runeson, who has visited the site of the Cassandra, confirmed that oil was already escaping from the wreck.
He said: “When we were on top of the wreck site, there were oil droplets coming up to the surface quite rapidly. We could see a new droplet coming up to the surface maybe every 15 seconds.”
In addition to the risk of oil pollution, the vessel is believed to be carrying paravanes — mine-clearing devices containing large quantities of mercury.
Mr Runeson said: “From oil leakage to mercury, it’s a totally different story in terms of how dangerous it is and the environmental consequences from it.”
In an effort to spur global coordination, Project Tangaroa has issued the Malta Manifesto, warning of a looming environmental crisis.
It warns: “We are entering a decade of severely heightened risk of catastrophic damage caused by oil from these wrecks — damage to natural and cultural heritage that cannot be fully remedied.”
The UK Government hopes the Cassandra mission will serve as a model for future wreck investigations and clean-up operations.
The Ministry of Defence’s Salvage and Marine Operations (SALMO) team will lead the expedition.
SALMO head Matt Skelhorn said: “With the survey of the Cassandra, we’re already putting into action the proof of concept for the Malta Manifesto.
“We look forward to sharing the survey outputs in due course, which will inform how we continue to work with the Estonian government to take action to prevent oil leakage if required.
“Cassandra has the potential to become a blueprint for future international collaboration when it comes to addressing the risks caused by potentially polluting wrecks.”
Project Tangaroa is backed by the Lloyd’s Register Foundation, The Ocean Foundation and Waves Group.
Mark Spalding, president of The Ocean Foundation, said: “We have thousands of environmental time bombs ticking on our ocean floor, with billions in remediation costs and no dedicated funding mechanism.
“The bureaucratic luxury of slow responses doesn’t match the environmental urgency — we need a Finance Task Force with the authority to act before 2039.”
The Cassandra sank on December 5, 1918, with the loss of 11 sailors. She lies on her starboard side at a depth of around 95 metres, with her bow blown off.
Mr Runeson said the wreck is otherwise remarkably intact, preserved by the low-oxygen environment — although corrosion is expected to accelerate.
He said: “Sooner or later, the Cassandra will rust up totally. Sooner or later, we have to deal with it, definitely.”