Aerial photo taken on April 15, 2020 shows the scenery of the Puma Yumco Lake in Nagarze County of Shannan City, southwest China's Tibet Autonomous Region. The frozen lake at an altitude of over 5,000 meters has started to thaw as the temperature rises in spring. (Xinhua/Purbu Zhaxi)

Aerial photo taken on April 15, 2020 shows the scenery of the Puma Yumco Lake in Nagarze County of Shannan City, southwest China's Tibet Autonomous Region. The frozen lake at an altitude of over 5,000 meters has started to thaw as the temperature rises in spring. (Xinhua/Purbu Zhaxi)

Aerial photo taken on April 15, 2020 shows the scenery of the Puma Yumco Lake in Nagarze County of Shannan City, southwest China's Tibet Autonomous Region. The frozen lake at an altitude of over 5,000 meters has started to thaw as the temperature rises in spring. (Xinhua/Purbu Zhaxi)

Aerial photo taken on April 15, 2020 shows the scenery of the Puma Yumco Lake in Nagarze County of Shannan City, southwest China's Tibet Autonomous Region. The frozen lake at an altitude of over 5,000 meters has started to thaw as the temperature rises in spring. (Xinhua/Purbu Zhaxi)

Aerial photo taken on April 15, 2020 shows the scenery of the Puma Yumco Lake in Nagarze County of Shannan City, southwest China's Tibet Autonomous Region. The frozen lake at an altitude of over 5,000 meters has started to thaw as the temperature rises in spring. (Xinhua/Purbu Zhaxi)

Aerial photo taken on April 15, 2020 shows the scenery of the Puma Yumco Lake in Nagarze County of Shannan City, southwest China's Tibet Autonomous Region. The frozen lake at an altitude of over 5,000 meters has started to thaw as the temperature rises in spring. (Xinhua/Purbu Zhaxi)

Aerial photo taken on April 15, 2020 shows the scenery of the Puma Yumco Lake in Nagarze County of Shannan City, southwest China's Tibet Autonomous Region. The frozen lake at an altitude of over 5,000 meters has started to thaw as the temperature rises in spring. (Xinhua/Purbu Zhaxi)