News channel Vesti-24 said the submersibles, Mir-1 and Mir-2, reached a depth of 1,680 meters (5,500 feet) in the world's deepest lake, which holds 20% of the planet's fresh water.
The ongoing expedition in what locals call the 'Sacred Sea' was organized by Artur Chilingarov, a Russian lawmaker who led a symbolic dive beneath the North Pole last August, during which a Russian flag was planted on the seabed.
Chilingarov earlier said the Mir dives were "a logical continuation of lake exploration that was begun 30 years ago with the Pisces apparatus."
Soviet scientists in a Pisces submersible reached a depth of 1,410 meters (4,600 feet) in 1977, and examined the lake's bed with searchlights. The lake has since been the focus of numerous Soviet, Russian and international research expeditions.
Chilingarov said "major technical problems" have to be overcome in deep dives into the lake, due to "difficult weather conditions which dictate their own special conditions in fresh water."
Baikal, whose age scientists estimate at 25 million years, is a UNESCO World Heritage site with hundreds of species of unique fauna and flora.
Crew member Natalia Komarova, the first woman to take part in a Mir mini-sub dive, told reporters that the results of the expedition would have an important impact on environmental legislation. (VIDEO)
"We need to understand how to protect Baikal and use it without harming its unique ecosystem," she said.
She said new safeguards would be needed to protect the lake, given the planned intensive economic and industrial development of East Siberia over the coming years. 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.
The research team is based on the lake's Olkhon Island, where the mini-subs were delivered earlier in the day on a barge. The crew includes the head of the local administration, and also the president of investment company Metropol, which has contributed $6 million to the expedition.
The expedition is set to run for two years, during which the scientists will conduct around 160 dives in various areas of the lake. Research will include tectonic information-gathering, and exploration for archeological artifacts. Expedition leaders have denied media reports that they will also be searching for oil and gas.
