Oil has leaked into the strait from two ships which ran into trouble during bad weather on 15 December. Volgoneft-239 ran aground following the storm, while Volgoneft-212 sank. Up to 5,000 tons of oil has now leaked, and media reports and official statements analyzed by BBC Verify suggest the spill has spread across the Black Sea and the Sea of Azov. A senior Russian scientist called the spill the country's worst "environmental catastrophe" of the 21st Century. "This is the first time fuel oil has been spilled in such quantities," Viktor Danilov-Danilyan — the head of science at the Russian Academy of Sciences (RAS) — said in a 17 January interview with a Russian newspaper. Russian scientists said in December that this spill could be more than twice the size of a similar disaster in the strait in 2007, which saw up to 1,600 tonnes of heavy oil leak into the sea. Ukraine's ministry of ecology has estimated that the clear up from the latest spill could cost the Russian state up to $14bn (£11.4bn). Paul Johnston, a scientist at Greenpeace Research Laboratories, said "there's always an element of uncertainty around oil spills", but a lack of timely information has heightened this uncertainty further. "I'm not entirely optimistic we'll ever know the full extent of the problem," he added. Satellite images reviewed by BBC Verify on 10 January — the most recent available high-resolution photos — showed a massive oil slick running through the strait, measuring at least 25km (15 miles) long. A second, smaller slick measuring around 5.7km (3.5 miles) long is also visible. Danilov-Danilyan said that oil could "by late January reach Odesa" in southern Ukraine and "one cannot rule out" it travelling as far as the coasts of Romania, Bulgaria and Turkey. In a statement to BBC Verify, a spokesperson for Greenpeace said the group estimated that oil from the spill now covered an area totalling up to 400 sq km. The spill appears to have moved quickly after the initial incident. On 24 December, satellite images reviewed by BBC Verify showed oil accumulating on a beach in Anapa — some 40 miles from the strait. A BBC graphic showing the spread of the oil towards Anapa. BBC Verify has analysed reports in Russian media, statements from officials and Greenpeace releases from this month that talk about oil being found or cleared up on various beaches. The reports suggest that the oil has now spread as far north as the occupied city of Berdyansk in Ukraine and as far south-west as Lake Donuzlav on the Crimean Peninsula, which Russian illegally annexed in 2014. The leak involves heavy M100-grade fuel oil that solidifies at a temperature of 25 degrees Celsius. A Greenpeace spokesperson told the BBC that M100 doesn't stay on the water's surface for long. Once underwater, it is "technically impossible to neutralise", and can take decades to be biodegraded by marine micro-organisms. Footage recorded by the Russian NGO The Earth Touches Everyone and included below appeared to show large amounts of heavy oil accumulating on the seabed. — BBC
