NOVOSIBIRSK, August 7 (RIA Novosti) - Scientists have located a crack in the bedrock of Siberia's Lake Baikal from which crude oil seeps into the lake, and have discovered a range of organisms living in the oil, an expedition member said on Thursday.

Researchers, who are currently examining the processes through which microbes in the world's deepest lake digest petroleum that naturally enters the water, conducted deep water dives on Monday and Wednesday to locate the oil source.

Dr. Mikhail Grachyov, an expert on the molecular evolution of Baikal's animal and plant life, said the source was found at a depth of around 850 meters (2,800 feet) to the south of Barguzin Bay, and that samples of the oil had been taken.

"It turns out that a large number of organisms live in this oil. This will require a huge amount of study," he told RIA Novosti.

"We will study everything - the oil, the means through which it is broken down, the microbes, physical characteristics, and so on. This is necessary both for fundamental science and for practical goals."

Research into Baikal's oil may provide new insights into the origins of petroleum, he said.

The consensus view among scientists is that crude oil is formed by decayed plant matter accumulating on the bed of a body of water and being subjected to heat and compression under heavy sediment over a period of millions of years.

However, several Russian scientists going back as far as Dmitry Mendeleyev have suggested an 'abiogenic hypothesis,' according to which petroleum was formed from carbon deposits originating deep in the Earth's mantle.

Baikal is the world's oldest lake, with an age estimated at 25 million years. Scientists taking part in the current expedition, during which 160 deep water dives are planned over the next two years, have stressed that research is not aimed at exploiting possible oil and gas reserves, but at protecting Baikal's unique ecosystem.

The lake has been the focus of major environmental scares in recent years, with a last-minute change to an oil pipeline route that was set to pass near Baikal's shores, and environmental regulators' claims against a pulp mill accused of pumping large volumes of toxic waste into the lake.

On Thursday the national environmental regulator Rosprirodnadzor said that after the Baikal Pulp Mill switches to a closed water cycle, which it is required to do by September 15, the regulator will also demand, through an arbitration court, that the mill stop burning solid waste.

Baikal, a UNESCO World Heritage site, holds around 20% of the planet's freshwater.