Russian news reports say two manned submarines have touched the bottom of Lake Baikal, the world's deepest body of fresh water.
The Interfax and ITAR-Tass news agencies on Tuesday cited expedition organizers as saying that the Mir-1 and Mir-2 submersible vehicles descended more than a mile (1,680 meters) to reach the bottom of the vast Siberian lake.
Scientists taking part in the mission are expected to conduct a host of geological and biological tests of Baikal. The lake is a UNESCO World Heritage site that is home to more than 1,700 species of plants and animals. It is the world's largest freshwater lake by volume.
Russia used the two submersibles last year during the controversial planting of a Russian flag on the bottom of the Arctic Ocean. Each of the vehicles carried three scientists.
The deepwater expedition has marked a new era in the history of Russia’s science.
The expedition to the depths of Lake Baikal was led by scientist Artur Chilingarov, who previously participated in the above-mentioned Arctic submarine mission on the North Pole.