Russia's Mir-1 and Mir-2 self-propelled deep submersibles started on Thursday the third stage of explorations of the world's deepest freshwater lake, Lake Baikal, in Siberia.

"The two Mir vessels will dive to a depth of around 900 meters. The duration of the dive will be 3-4 hours," Roman Afonin, Executive Director of Fund for the Protection of Lake Baikal said.

The third stage of the scientific and research expedition on Baikal's southern region will last from July 1- September 5.

World War II veteran Valentin Kazantsev, an 83-year-old sailor, will join the expedition during one of the dives.

During the first stages of the expedition in 2008 and 2009 the manned submersibles already committed more than 160 submersions. The objective of the program is to research and monitor the ecosystem in the lake.

Last August, Russian Prime Minister Vladimir Putin made a 4-hour dive in the Mir-1 submersible to a depth of 1,395 meters (over 4,500 ft) of the lake. In a radio conversation to journalists above the surface, Putin said he was surprised the lake was not as clear as he had earlier thought at that depth, calling it "a plankton soup."

The organizers of the expedition have planned a dive a submersion near Olkhon Island, where the depth is more than 1,600 meters, the deepest area in Lake Baikal, which would set a new world record for freshwater submersion.

IRKUTSK, July 1 (RIA Novosti)