The US-Israel war on Iran is increasingly being fought at sea, with both sides targeting oil tankers and other vessels in and around the Strait of Hormuz.

On September 8, the United States struck five Iranian oil tankers, provoking a counterattack on Jordan’s al-Azraq airbase.

Just three days earlier, the US had hit three Iranian tankers. Those strikes came after Iran launched ballistic missiles towards a US aircraft carrier and a navy destroyer near the strait, according to US Central Command (CENTCOM). Iran also subsequently said it had targeted three oil tankers travelling through what it called an “unauthorised route” in the strait, as well as three US-linked vessels elsewhere.

The tit-for-tat attacks have turned Hormuz into a potential environmental tinderbox. With tankers carrying millions of barrels of crude oil and petroleum products passing through or waiting around the waterway, a successful strike could trigger a fire, sinking, or a major oil spill.

Oil tankers trapped around Hormuz

As of Monday, MarineTraffic data shows 42 tankers waiting to transit the Strait of Hormuz, while hundreds of other vessels are waiting or moving slowly in the wider Gulf of Oman and the Gulf region. Of those tankers, 18 are carrying oil.

While it is not known exactly how much, if any, crude they were carrying, these vessels have an estimated combined capacity of 1.76 million cubic metres of oil and petroleum products - cargo that could be at risk if attacks on commercial shipping continue.

How much oil is that?

That - 1.76 million cubic metres of crude oil - is roughly 11.1 million barrels of oil, and is equivalent to about 11 percent of the world’s daily oil demand, enough to fill roughly 714 Olympic-sized swimming pools.

Now imagine the environmental damage. A major tanker strike or sinking could release millions of litres of oil into the Gulf, potentially contaminating coastlines, fisheries and fragile marine ecosystems.

Unlike land, oil at sea can spread over a vast area, carried by currents and winds far from the original site of the spill.

How many ships have been hit in recent days?

On September 5, CENTCOM said its forces struck three Iranian oil tankers - one off Kharg Island, Iran’s main oil-export hub; another near Jask; and a third, an unladen tanker, in the Gulf of Oman after its crew was ordered to abandon ship.

The strikes marked a new escalation in attacks on oil shipping in the region.

Since the start of the war, at least 75 ships have been attacked, with at least 21 seafarers killed. Of those vessels, two incidents have resulted in minor oil spills, while six have caused fires.

A spill already spreading off Oman

Oil has been leaking from the Caroline Bezengi since it ran aground about 22 nautical miles (41km) off Oman’s coast after its crew reported a suspected explosion in early June. The Reuters news agency estimates the tanker was carrying 800,000 barrels of oil.

Oman’s Environment Authority warned that the spill could affect about 40km (25 miles) of coastline near Ras Madraka, as well as Masirah Island.

On August 3, the Minoan Pioneer, a Liberian-flagged bulk carrier, was struck by an unidentified projectile off Oman and caught fire.

Satellite imagery taken on August 10 showed a large slick near Qeshm Island, while another slick was detected near Sirri Island. Experts said the Qeshm slick likely came from the Minoan Pioneer, but could not independently confirm its source.

What is the impact of the attacks on tankers on marine life?

Fares al-Momani and Ponnumony Vethamony, researchers at the Environmental Science Center at Qatar University, told Al Jazeera that chronic oil pollution has been an intense burden in the Gulf since the 1980s.

“The region has undergone drastic economic, social and industrial development, and the coastline has been modified and extensively developed to host desalination plants, power plants, oil rig platforms, refineries, and other coastal infrastructures,” they said, responding jointly in an email. “Consequently, the Gulf has become one of the most anthropogenically impacted marine regions in the world.”

Past conflicts like Operation Desert Storm - in which the US fought Iraq after Saddam Hussein’s forces had invaded Kuwait - also left a legacy of environmental pollution.

As Iraqi forces retreated, they set Kuwaiti oil wells on fire. These burned for months and unleashed millions of gallons of oil into the northern Gulf coast, which damaged Kuwaiti and Saudi Arabian coastlines for decades.

More than 770km of coastline from southern Kuwait to Abu Ali Island in Saudi Arabia were engulfed in oil and tar, wiping out the local marine ecosystems.

The damage from the oil spill was colossal, destroying coastline sediments, marine species and ecosystems.

Al-Momani and Vethamony said the scale of the Gulf War oil spill was so vast that “the cleanup was more focused on damage control than restoration”, in comments they jointly shared.

Now, 35 years later, the US-Israel war on Iran has again imperilled the fragile marine ecosystem. US air strikes have pounded Iranian vessels and oil tankers near Iran’s coastline. Tehran has retaliated with similar strikes against ships and tankers from other countries.

A study by the University of South Florida in June found that, based on satellite imagery, the oil spills in the Gulf and the Strait of Hormuz were four times as much in March than the year before.

The research team noted high instances of oil leaks from vessels trapped in the strait and around trapped vessels.

Oil spills lie on top of the water, damaging and poisoning marine life, polluting the water and smothering coral reefs and mangroves.

The Gulf contains resilient coral reefs and mangrove forests that survive in one of the world’s hottest and most saline marine environments.

The enclosed water is a shallow, semi-enclosed sea supporting coral reefs, seagrass beds, mangroves, mudflats and salt marshes.

These habitats are critical feeding and nursery grounds for fish, turtles, dugongs and migratory birds, while supporting fisheries and protecting coastlines.

With limited water exchange with the wider Indian Ocean, pollution can add to the pressure on the Gulf’s marine ecosystems.

Hussein Samh al-Masroori, associate professor at Sultan Qaboos University in Muscat, Oman, said oil and petroleum hydrocarbons can directly affect fish, corals, plankton and other marine organisms. Fish eggs and larvae can be particularly vulnerable.

“Sensitive habitats such as coral reefs, mangroves, seagrass beds and coastal sediments may retain pollutants for much longer,” he told Al Jazeera.

“There can also be indirect effects through changes in water quality, food-web productivity, fish distribution and potentially spawning or migration patterns. For fisheries, this can translate into reduced fishing opportunities, higher costs and loss of income for coastal communities.”

The Gulf countries primarily rely on desalination as the primary source of water for the entirety of their nearly 65 million people. Iran also has several desalination plants along its southern coast, some of which have come under attack by the US. Approximately 15 million people live along the coast of Iran.

Al-Masoori explained that oil contamination can affect the quality of the raw water that desalination plants take in, interfere with treatment processes and, in severe situations, require temporary operational restrictions.

“The actual risk depends greatly on the location of the spill, currents, distance and depth of the intake, and treatment technology,” said al-Masoori.

However, he added, modern monitoring, modelling and advanced treatment systems can substantially reduce the risk. The priority is early detection, so contaminated water can be prevented from entering desalination systems.

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