Why might the Angara River be considered the upper course of the Yenisey system?

The Angara River is often considered a candidate for the upper course of the Yenisey River system rather than a mere tributary for several hydrological and geographical reasons:

• Volume and Basin Size: The Angara possesses a greater volume of water at its mouth than the Yenisey does above their confluence. Furthermore, the Angara’s own drainage basin covers more than 407,700 square miles (1,056,000 square km), which is twice the size of the Yenisey’s basin above the point where the two rivers meet.1
• Hydrological Regulation: Unlike the Yenisey, which is fed primarily by rainwater and melting snow and experiences significant seasonal fluctuations, the Angara is highly regulated by its source, Lake Baikal. Consequently, the Angara rarely experiences low-water periods.1
• Ultimate Source: When considering the entire system, the headwaters of the Selenga River—which flow through Lake Baikal into the Angara—are sometimes identified as the ultimate source of the Yenisey. Including this path significantly increases the total length of the river system to 3,442 miles (5,539 km).2