The UN began 19 day operation extracting oil from a 47-year-old crumbling supertanker trying to end a race against time to avoid a catastrophic oil spill.

The tanker, named Safer, has been stranded off Yemen’s Red Sea coast more than eight years after civil war broke out in the Middle Eastern country. Since 2015, the conflict has prevented the vessel, which contains 1.1 million barrels of oil, from undergoing maintenance.

This led to growing fears of a possible oil spill four times larger than in 1989 Exxon Valdez spill, which was the second largest oil spill in US history.

The UN estimates that a potential cargo spill from the Safer tanker would result in $20 billion in clean-up costs, have a “severe” environmental impact on Yemen’s coastal water and reefs, and disrupt the Bab al-Mandab strait of the Suez Canal.

It would take 25 years for the local fish population to recover, the UN added.

The oil on board the tanker began being transferred to the UN-owned vessel Yemen, formerly known as Nautica, at 10:45 a.m. Yemen time on Tuesday.

The operation still poses significant risks as it takes place in open waters and the infrastructure of the Safer tanker is heavily corroded.

“The @UN has launched a complex operation to remove 1 million barrels of oil from a decaying tanker off the coast of Yemen. We must continue to work to defuse what remains a ticking time bomb and avoid what would be by far the worst oil spill of our era,” UN Secretary-General Antonio Guterres said on social media platform X, formerly known as Twitter, on Tuesday.

“The transfer of oil to Yemen will prevent the worst-case scenario of a catastrophic spill in the Red Sea, but it is not the end of the operation,” said David Gressly, UN resident and humanitarian coordinator for Yemen. “The installation of the CALM buoy, to which the replacement vessel will be securely moored, is the next crucial step.”

The UN launched its initiative to rescue oil from the Safer tanker in 2019, but has struggled to gain access to the vessel from Yemen’s Houthi rebel group.

“The derelict supertanker FSO Safer and its 1.1 million barrels of oil cargo has been a ticking time bomb since 2015, threatening humanitarian, environmental and economic disaster, it is only the heroic efforts of a small core crew and the sheer luck that disaster did not happen,” said Ghiwa Nakatexecutive director of Greenpeace MENA, 23 July. “While a rescue operation has its risks, they are less than doing nothing.”