Hiiumaa wrecks hold thousands of litres of heavy fuel oil

German warships sunk off Hiiumaa during the First World War still contain significant amounts of heavy fuel oil, which could pollute the coasts of Estonia, Finland and Sweden if it leaks, ERR reports.

Researchers from the Estonian Maritime Museum and Finland, led by Ivar Treffner, assessed the wrecks of German torpedo boats S57, V72 and V75. The ships sank in November 1916 after unexpectedly hitting a minefield during an unsuccessful attack on Paldiski harbour.

As navies were then beginning to switch from coal to liquid fuel, the ships took thousands of litres of heavy fuel oil down with them. The wrecks are not currently leaking, and their hulls are not expected to collapse in the near future. But the longer the metal deteriorates on the seabed, the harder it will be to recover the oil safely.

The wrecks have been preserved by the Baltic Sea’s low salinity, cold temperatures and limited oxygen. The sea also has very few oil-degrading bacteria. These conditions help preserve the wrecks while keeping potential pollution contained inside their hulls.

Specialists say the risk should be addressed quickly to prevent the oil from reaching coastal waters. The researchers published their findings in the journal Heritage.