How long does ice cover remain on the upper and lower Ob River?

The ice cover on the Ob River varies significantly between its upper and lower reaches due to the river's vast length and climatic range. The upper reaches of the river remain frozen for approximately 150 days, while the lower reaches remain frozen for about 220 days.1

Ice typically begins to form on the river between the end of October and the second week of November, with the entire river becoming frozen by the last week of November. The thawing process, which generally takes longer than the initial freezing, occurs from the end of April in the upstream sections to the end of May in the lower reaches.1