The mass death of hundreds of sea creatures in Russia's far east has been blamed on toxic algae by officials.
Fears were raised weeks ago that the incident could have been caused by a major marine pollution incident on the pristine Kamchatka peninsula, but Russian ministers have denied such claims.
“This is not a man-made disaster,” Dmitry Kobylkin, the environment minister, told state-owned Rossiya 24 television channel on Friday.
“We didn’t find any leaks, any oil or any significant increase in fuel that could have caused the deaths.”
The Russian Investigative Committee that deals with high-profile crimes said in a statement they found no heavy metals or fuel in the dead sea creatures or water samples.
They believe that the deaths were likely caused by "phytoplankton blooms".
Earlier this month surfers posted videos of a yellow-tinged sea, whilst photographs from tourist hotspot Khalaktyrsky Beach showed the sand strewn with dead sea urchins, octopuses, seals and fish. Hundreds of creatures were reportedly killed and an area as large as 25 miles has been affected.
Surfers also reported damaged eyesight and poisoning symptoms.
Officials were investigating a possible toxic leak and some pointed to two local military testing sites. Svetlana Petrenko, the Investigative Committee’s spokeswoman, said on Friday that those who sought medical treatment did not show any signs of poisoning.
Mr Kobylkin said authorities want to investigate why the algae was so toxic.
While Russian authorities describe the harmful algae as a “natural” cause, scientists have pointed to global warming and nutrient pollution as the main reason behind a recent surge in the growth of toxic algae blooms around the world.
Greenpeace last week published a report following its expedition to Kamchatka, saying that “none of the compounds found in the samples by the Russian authorities or Greenpeace Russia could cause such serious consequences".
The environmental group named a man-made disaster and “natural” factors as a probable cause of the massive die-off and demanded an independent investigation.
Greenpeace said that long-term effects of what it described as an environmental disaster would be clear next year when sea otters and other mammals would face a shortage of food such as sea urchins.