Swedish authorities have seized an oil tanker suspected of belonging to Russia’s “shadow fleet” after it allegedly caused a significant oil spill in the Baltic Sea.

An aircraft belonging to the Swedish Coast Guard detected a 12-kilometer oil spill just east of the island of Gotland. Authorities estimate that at least 2,000 liters of oil have leaked into the water, though there is currently no immediate risk of it washing ashore.

In a joint operation with local police, the Coast Guard seized the tanker Flora 1, which is believed to be the source of the leak. While the ship is registered in Sierra Leone, its true ownership and flag status remain deliberately obscured, and the vessel is actively on the European Union’s sanctions list.

Swedish officials noted that the Flora 1 is the same model as several other vessels they have intercepted over the past month. European nations accuse Russia of using a “shadow fleet”—a covert network of aging, substandard ships—to bypass international sanctions imposed over the war in Ukraine.

An investigation into environmental crimes has been officially launched. While no one has been taken into custody yet, authorities have indicated that at least one member of the ship’s crew will be brought in for questioning.