Aerial photo taken on March 6, 2021 shows a herd of sheep walking along a safe path on the frozen Puma Yumco Lake during their annual migration in southwest China's Tibet Autonomous Region. (Xinhua/Jigme Dorje)

LHASA, March 10  -- Migrating to pastures new in the depths of winter is tough, but traveling across a frozen lake with thousands of sheep in tow poses extra challenges, and that is exactly what is happening at Puma Yumco Lake, one of the world's highest lakes.

In the coldest time every year, at Dowa village, 5,070 meters above sea level, thousands of sheep are taken across frozen water to islands on Puma Yumco Lake. Herders usually spend a month with the animals on the islands, where grass grows to waist height.

When spring draws near, the herds of sheep will be taken back to their former habitat, by walking across the frozen lake again before the melting of the ice. Such herding practices have lasted for a thousand years at Dowa village.