After six hours of driving northeast from Irkutsk, the Cousteau vehicles finally crossed the last pass that hung over Lake Baikal. An immense white desert stretched to the horizon where the beige mountains of Olkhon Island separate the lake into two parts: on the eastern side, the “little sea” and on the western, the “great sea” that extends 650 kilometers from north to south.

This deepest and oldest lake in the world lies on the border of Russian Siberia and Outer Mongolia. Known as the “Pearl of Siberia”, the lake fills a tectonic trough that is widening at the rate of 2.5 cm a year, swallowing up sediment and leaving crystalline water above. In 1997, the Cousteau team travelled the lake to film the rich, diverse life in it: 1,800 species of which 80 percent are endemic (the omul salmon, the oily golomyanka fish and the freshwater seals called nerpas).