Dr. Mikhail Grachyov, an authority on the molecular evolution of the unique flora and fauna of the world's deepest lake, said the research team began on Monday a search for cracks in the rock that release around four metric tons of oil into the lake each year.
"Baikal has microbes that absorb this oil, so it does not spread through the lake, but is localized. It is important that we study these processes more thoroughly," he told RIA Novosti.
Monday's descent in the Mir-1 and Mir-2 mini-submarines, part of a series of deep-water dives that began last week, failed to locate an oil source, known to be at a depth of around 800 meters, he said.
"We haven't managed to locate the actual oil source, it's not easy to do this," Grachyov said. However, the submersibles did discover an old fissure that had previously released oil.
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.
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.
Baikal, a UNESCO World Heritage site, holds around 20% of the planet's freshwater.
