Russia has opened a criminal investigation into unexplained toxic marine pollution off its far eastern coast.
Whole populations of sea life have been wiped out in the region's waters with carcasses washing up on the shores of the Kamchatka peninsula.
Local surfers and divers have also reported health issues with their eyes and throat after entering the water.
Environmental campaigners from Greenpeace have described the situation as an "ecological disaster" and have observed "yellowish foam" at the surface of the water.
On Wednesday, Russia's Investigative Committee confirmed in a statement that it was investigating the contamination in the Avacha Gulf for the "circulation of environmentally hazardous substances and waste".
Initial findings suggest that the contaminant in the water closely represents the consistency of "industrial oil or other substance that contains oil-containing components".
Authorities have confirmed all possible sources of the pollution are being investigated, including a nearby facility used to store pesticides and local landfill sites. No suspects have been named in the investigation.
The regional ecology ministry in Kamchatka announced that environmental supervisors inspected the Radyginsky military storage facility, but found no pollution.
"There are no other premises for toxic chemicals or storage of other hazardous substances that could be the cause of contamination," said Valery Simakov, head of the regional inspection of the state environmental supervision.
The Investigative Committee noted that dead marine life had washed up on the shores of the volcanic peninsula between September 1 and October 3.
The law enforcement agency also said that the water had been found to contain oil components including phenol and had changed colour.
Two surfers were confirmed to have received chemical burns on the cornea of their eyes as a result of being in the water.
Dmitry Kobylkin, Russia's minister of natural resources and the environment, said on Wednesday that those responsible for the pollution would be punished.
“There cannot be any compromises here, as with the situation in Norilsk,” he said, referring to a major fuel spill in the Russian Arctic in May.
“Citizens’ environmental well-being and the preservation of ecosystems come first.”
Kobylkin had initially said that water and land samples showed no evidence of high levels of oil products and that the pollution did not appear to be manmade.
Russia's Pacific Fleet headquarters have denied any involvement in the environmental crisis, and authorities have refused to rule out that the pollution could have caused by natural phenomena.