(CNN) — An oil spill from a stranded tanker off the coast of Oman now covers an estimated 500 square miles (1,300 square kilometers), the environmental organization Greenpeace told CNN, prompting fears that a major ecological disaster could be unfolding in the Arabian Sea.
The spill has spread to mainland Oman, roughly 120 miles (200km) from the tanker, according to Omani authorities.
Greenpeace campaigner Hanen Keskes said their analysis of satellite images showed fragmented spots, meaning the spill is in multiple areas rather than one continuous mass.
The Omani government is yet to confirm the size of the impacted areas. Its environment authority did not respond to questions from CNN.
The government instructed citizens to avoid fishing in affected areas and to report unusual odors and oil sightings. It also said it would test seafood in markets to check for pollutants.
International salvage efforts are underway, involving vessels and aircraft “with over 100 tons of equipment,” according to British maritime security company Ambrey. But the operation is being hampered by the annual monsoon season known as “Khareef.”
The tanker, Caroline Bezengi, was carrying around 800,000 barrels of oil when it reportedly came under attack. The sanctioned vessel is believed to be part of the shadow fleet of oil tankers used by Russia.
An unknown cause
Following an unidentified “incident” on June 6 outside Oman’s territorial waters, the tanker ran aground off Al-Qibliyyah Island on June 21, Abdullah Bin Ali Al Amri, the chairman of the Environment Authority of Oman, told state TV earlier this week.
While some security observers reported an explosion on board the ship, the exact nature of the incident hasn’t been determined. The tanker had left one conflict zone – Novorossiysk, a Russian port city on the Black Sea, where Ukraine has targeted Russian vessels – before traveling close to Yemen, where the Houthis have attacked ships as part of the Iran-US conflict.
The leakage of stored oil was first detected in the first week of July, Al Amri said. By August 4, the spill had spread across roughly 230 square miles (600 square kilometers) in the Al Hallaniyat archipelago, representing “a fourfold increase over just the last two days,” according to Greenpeace’s analysis of satellite images.
“This is one of the most ecologically significant marine areas in the region,” Keskes said. “It includes things like coral reefs, seagrass, meadows, nesting beaches for endangered turtles, breeding sides for migratory seabirds, and it’s also home to the Arabian Sea humpback whale, which is an extremely rare creature.”
On Wednesday, Omani authorities said the spill had drifted to reach the mainland, affecting 25 miles (40km) of the Ras Madrakah coastline, more than 124 miles (200km) away from the tanker. As it began to drift further northeast, the spill was also expected to affect Masirah Island, according to the Omani environment authority.
This development may have a more lasting impact on communities along the coastline. Once oil reaches the shore, “not only does the containment becomes that much harder, but basically [the oil] goes into the sediments and the water … and it becomes embedded for years even after the spill has disappeared,” Keskes explained.
The spill also carries numerous health risks for coastal communities, especially those relying on fishing, she added.
Shadow fleet dangers
Further north in the Strait of Hormuz, Iran has also reported an oil spill affecting Qeshm Island and demanded compensation for the environmental damages. The cause of that spill is unknown.
In addition to the ongoing conflict which has seen multiple vessels attacked across the region, the increase in shadow fleets carrying sanctioned oil is exacerbating the danger of environmental damage.
These vessels are “unregulated and often happen to be decrepit” and fall outside the legal chain of liability, Keskes explained. “In normal non-war-related incidents, something like [the Oman spill] happens, you would have to look at the owner of the ship and then their flag and the insurer. But all three are either unclear or just missing.”
This means the response and the hefty cost of damages will fall entirely on the Omani government, she added.
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