Oil Slicks Visible From Space as Tanker Strikes Threaten Gulf Ecosystems for Decades

From orbit, the slicks in the strait of Hormuz show up as vast dark stains on the water. Through October, oil tankers in the waterway were hit by missiles or sea mines, and crude poured out of them. The pollution has since spread across the Gulf, reaching coastlines and threatening ecosystems that shelter dolphins, sea turtles and countless fish species.

The war between the US and Iran began on 28 February, and eight months in, one of the world's busiest oil shipping routes has become a battlefield. A naval blockade of the strait makes documenting the damage from the ground almost impossible, so the picture has to be assembled from satellite images, environmental experts and marine biologists.

Greenpeace has used satellite monitoring to identify more than 500 oil spills across the Gulf, the strait and the Arabian Sea since the war started. Some are tied to attacks on vessels; others were detected around the time of strikes, but their origins could not be confirmed. Nina Noelle, a Greenpeace expert on environmental disaster relief, said that adding up the daily mapped footprints gives a cumulative area of roughly 20,000 square kilometres, almost the size of Wales. Greenpeace counts more than 133 attacks on oil tankers since the conflict began. The Washington Institute for Near East Policy reports that October was the worst month, with more than 30 confirmed or reported attacks in and around the strait. They have continued into November.

Several incidents stand out. The strike on the supertanker Gem No 2 off the United Arab Emirates left a slick more than 21 miles (35km) long, and a satellite image from 19 October shows black oil moving into clear water off Umm Al Quwain. Greenpeace estimates that a tanker attack in early June produced a slick off Oman covering more than 600 sq km at its peak. Two Iranian naval vessels hit in March kept leaking for months, according to Wim Zwijnenburg of the Dutch peace organisation Pax. An attack on the Liberian-flagged Minoan Pioneer on 3 August has also been linked to a major slick.

Oil has reached shorelines repeatedly. In March, a slick from the Shahid Bagheri was detected near the Hara mangroves. In April, pollution threatened Shidvar Island, a protected site with coral reefs, seabirds and turtles. In August, oil was reported washing ashore at Qeshm Island, near important fishing grounds and turtle nesting sites. Satellite imagery also shows slicks near Oman's Musandam national park and Iran's Minab River delta, both rich in wildlife.

Responsibility is tangled. Iran's Islamic Revolutionary Guard Corps has been blamed for most of the attacks. US forces have also targeted tankers, disabling Iranian vessels trying to cross the American blockade and striking others in response to Iranian missile attacks on US warships. A Wall Street Journal report says the largest spill came from a UAE air force strike on oil storage tanks on Lavan Island, which sent crude into the Gulf and affected coastal areas including the Shidvar Island reserve nearby.

Governments have responded in places. After the Gem No 2 attack, the UAE closed beaches, launched a major cleanup and monitored its desalination plants; on 30 October authorities said the leak had been stopped and pollution was declining. In Oman, divers and equipment were sent to a damaged vessel, and crews cleared oil from 7 miles of coastline near the Hallaniyat Islands.

The longer-term concern is harder to contain. Noelle warned that oil can stay trapped in sediments, shorelines and mangrove roots after the slicks vanish, harming food chains and fishing communities. Mangroves and reefs can take decades to recover, she said, and repeated spills risk worsening the damage. Oil can coat birds' feathers and smother mangrove roots. Bernhard Riegl, a Nova Southeastern University marine biologist who has studied the Gulf for over 30 years, points to history: a 2020 study traced tar on Qatari beaches to the Gulf war, and a 2022 study found sediment on Saudi Arabia's Abu Ali Island still contaminated by the 1983-85 Nowruz spills, which released 80m gallons. The Gulf is shallow and already stressed by heat, he noted. "We could really lose something irreplaceable," he said.

The full toll remains unknown. Investigations on the ground are extremely difficult, and some researchers in Iran and Gulf states said domestic authorities told them not to speak publicly about the war's environmental damage.