Why can the Yenisey River be measured at different total lengths?

The total length of the Yenisey River varies depending on which headstream is identified as the river's source. Because river systems are complex, different geographical interpretations of where a river "begins" lead to different measurements.12

The primary variations in the Yenisey's length are as follows:

• From the confluence: If measured from the city of Kyzyl, where the Great and Little Yenisey rivers meet, the river is 2,167 miles (3,487 km) long.1
• Including the Great Yenisey: If the Great (Bolshoy) Yenisey is considered the source, the total length increases to 2,540 miles (4,090 km).1
• Including the Selenga system: If the headwaters of the Selenga River—which flow through Lake Baikal and into the Angara River tributary—are considered the ultimate source, the system reaches a total length of 3,442 miles (5,539 km).12

These discrepancies highlight the difficulty in establishing definitive river lengths, as scientists and geographers often debate the criteria for identifying the most distant source of a river system.32