The First Detailed Survey and Assessment of HMS Cassandra: A Site of Underwater Cultural Heritage, Potentially Posing a Significant Risk to the Environment

In the summer of 2025, the first thorough archaeological research of a potentially polluting wreck HMS Cassandra was carried out in Estonia. HMS Cassandra , which sank in 1918 was a British light cruiser with a maximum capacity of about 1100 cubic meters of fuel oil. The research included a high-resolution multibeam survey combined with the creation of a photogrammetric model of the wreck. The gathered data, compared to the ship’s original assembly plans, was used to assess the current state of the wreck and to calculate the potential quantity of fuel still on board. Research showed that in the worst case scenario the wreck could still hold more than 800 cubic meters of oil making it the highest risk wreck in Estonian waters, from an environmental perspective. Three different spill scenarios were simulated to calculate the drift of oil and the areas affected by it. This project showed the importance of international cooperation between the Flag State and the Coastal State in mitigating the environmental risk posed by the wreck.