Altan Gadas

Altan Gadas belongs to the Selenga river country of northern Mongolia. The river forms where the Ider and Delger meet and then runs roughly 992 to 1,024 kilometres before entering Lake Baikal. Its basin is a semi-arid region covering about 280,000 square kilometres, with scattered forests and extensive mountain ranges. Because the Selenga reaches Lake Baikal through the Angara, it forms part of the most distant headwaters of the Yenisey–Angara river system. Climate strongly influences the river.

The Siberian High brings harsh winters, and the water generally freezes from November to April. Warmer summers produce annual floods whose size can range from ordinary to catastrophic. At its mouth the river creates a delta of about 680 square kilometres and supplies almost half of the riverine water entering Lake Baikal. The basin also contains a long record of human activity.

Paleolithic sites such as Ust-Kyakhta-3 show that people lived along the Selenga from the Stone Age. The river connected mountain pasture, forest steppe and routes northward through Buryatia. Its channels were an axis for movement and settlement, while the delta's wetlands sheltered many birds and provided habitat for species including the Baikal sturgeon.