Environmental groups have said the damage caused by oil leaking from two stricken Russian tankers in the Kerch Strait could have a devastating impact on marine life in an area where any cleanup effort will pose an immense challenge.

Natalia Gozak, director of Greenpeace Ukraine, said the environmental repercussions could end up on par with the wide-scale flooding caused by the June 2023 explosion at the Kakhovka dam in southern Ukraine while it was under Russian control. The destruction of the dam flooded a zone the size of Kyiv, wiping out wildlife and more than half a million hectares of natural habitats a releasing potential pollutants from more than 1,000 flooded sites.

"This is rather comparable for the huge environmental impact in this area," Gozak said, speaking with DW from Kyiv. She stressed it was too soon to know the full extent of the oil spill and that the ongoing Russia-Ukraine war made it extremely difficult to assess the situation.

But, she added, with environmental cleanup likely not high on the list of Russia's concerns in the region, "wildlife, fauna … and the well-being" of future human generations were all at risk in the Kerch Strait.

The two oil tankers, together carrying around 9,000 tons of heavy, low-grade fuel oil, were caught up in a storm on Sunday and severely damaged in the Kerch Strait, which separates Russia and the annexed Crimean Peninsula in Ukraine. It's a key route to the Black Sea for Russian shipments of grain and fuel and a supply route in Moscow's war against Ukraine.

One vessel had its bow torn away and was seen partially submerged and surrounded by an oil slick in an unverified video circulating on Ukrainian and Russian social media channels.

The other tanker ran aground some 80 meters (about 260 feet) from shore near the Russian port of Taman. Russian investigators said on Monday that they had opened two criminal cases to probe possible safety violations.

Officials had yet to assess the full impact of the oil spill, but preliminary estimates reported by Russian state news outlet RIA Novosti said around 3,700 tons of fuel oil had leaked into the sea. In a statement on Telegram on Tuesday, Governor Veniamin Kondratyev, the leader of Russia's Krasnodar region, said some of the oil had now reached the shore.

"This morning, while monitoring the shoreline, stains of fuel oil were discovered. Oil products washed ashore for several tens of kilometers," he said. Local media also posted videos of the beach with a black, oil-like substance and birds covered in oil struggling to fly.

Winter storms will make environmental cleanup difficult

Ukrainian officials, who have no direct access to the area, have said the winter storm season will likely make it challenging for Russia to recover the tankers. They also implied the ships had no business being at sea.

"The Russians have a rather complicated situation ... in the Azov and the Black Sea region. They use an outdated fleet: these ships were more than 50 years old," Ukrainian navy spokesperson Dmytro Pletenchuk told national media. He said the ships involved in Sunday's accident were designed to be used along rivers and to load other seagoing vessels and were not intended for use in stormy weather.

According to Gozak of Greenpeace, experts who analyze tracking data say the ships were normally used to navigate rivers and coastal waters and had turned off their AIS global naval navigation system in the days leading up to the accident, which the Ukrainian Navy also confirmed. Gozak said it's possible the ships were being used to deliver fuel for military purposes, adding that it was impossible to verify.

She compared the disaster to a similar incident in November 2007, when another Russian tanker split in two during a storm and leaked some 1,300 tons of oil and other pollutants in the same area. That disaster contaminated several dozen kilometers of coastline in both Ukraine and Russia, killing tens of thousands of birds and other marine life. But she said this latest spill, at some three times the size, could be much worse.

"Any oil or petrochemical spill in these waters has the potential to be serious," said Paul Johnston, who heads Greenpeace Research Laboratories in the UK, in a statement. The science unit of Greenpeace International provides scientific advice and analytical support to the environmental group's campaigns worldwide.

"In the current weather conditions, [it] is likely extremely difficult to contain. If it is driven ashore, it will cause fouling of the shoreline, which will be extremely difficult to clean up," said Johnston. And, he added, if the ships sink it could see the release "of oil and petrochemicals over a longer time span."

Hugo Nijkamp, a marine biologist with the Brussels-based oil spill response organization Sea Alarm, agreed that any cleanup effort will be difficult.

"The main problem is that the area is considered a war zone, so no resources from abroad will be available for mobilization because of security reasons," he told DW by email, adding that a lack of resources in the region meant it was "unlikely" that wildlife affected by the oil spill will be given the necessary care.

"Self-mobilizing citizens may undertake some action, but results from such spontaneous initiatives are never promising," he said.

Russia's aging 'shadow fleet' a disaster 'waiting to happen'

In an X post on Monday, Mykhailo Podolyak, an adviser in the office of Ukrainian President Volodymyr Zelenskyy, blamed the accidents on "two rusty vessels" and linked the oil spill to Russia's so-called "shadow fleet," which he said were "hopelessly outdated, have fictitious insurance policies, conceal their true owners, and often overload oil at sea."

In October, the Kyiv School of Economics Institute warned that Russia's shadow fleet was an "environmental disaster … waiting to happen in European waters."

So far, there's been no indication that the ships involved in Sunday's disaster were part of this shadow fleet. Russian officials have released little information about the ships besides confirming the spill and the rescue operation.

But the Helsinki-based Centre for Research on Energy and Clean Air (CREA) said Russia's shadow tanker activity had risen significantly in 2024, with "an average of three 'shadow' tankers carrying Russian crude oil departed daily from Russian ports" in the first eight months of 2024.

In an October 2024 report, CREA said the tankers often navigate "high-traffic routes through narrow straits close to shorelines, with their automatic identification system [AIS] turned off to conceal their location."

The report estimated that cleaning up after a disaster involving one of these tankers could cost as much as $1.6 billion (€1.5 billion) — a bill that would almost certainly fall to coastal countries to pay.

Edited by: Tamsin Walker