It is one of the coldest points of the year in Tibet and time for a risky, exhilarating annual affair - the migration of sheep across an icy lake.

Every winter, villagers herd thousands of sheep across the Puma Yumco lake's frozen surface (pictured above in a drone shot taken last week) to two small islands, where the soil is more fertile and the forage is better in the winter.

Several hundred lakes dot the expansive Tibetan Plateau, and Puma Yumco in Lhozhag County is one of the larger lakes in southern Tibet. With the average plateau elevation exceeding 4,500m above sea level, the plateau's lakes are among the highest in the world, according to the Nasa Earth Observatory.

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