People take a walk at Lhalu wetland in Lhasa, southwest China's Tibet Autonomous Region, on April 7, 2019. Lhalu wetland national nature reserve, with an altitude of 3,645 meters, covers an area of 12.2 square kilometers and is known as "the Lung of Lhasa." (Xinhua/Zhang Rufeng)

Birds are seen at Lhalu wetland in Lhasa, southwest China's Tibet Autonomous Region, on April 7, 2019. Lhalu wetland national nature reserve, with an altitude of 3,645 meters, covers an area of 12.2 square kilometers and is known as "the Lung of Lhasa." (Xinhua/Zhang Rufeng)

Birds are seen at Lhalu wetland in Lhasa, southwest China's Tibet Autonomous Region, on April 7, 2019. Lhalu wetland national nature reserve, with an altitude of 3,645 meters, covers an area of 12.2 square kilometers and is known as "the Lung of Lhasa." (Xinhua/Zhang Rufeng)

A bird is seen at Lhalu wetland in Lhasa, southwest China's Tibet Autonomous Region, on April 7, 2019. Lhalu wetland national nature reserve, with an altitude of 3,645 meters, covers an area of 12.2 square kilometers and is known as "the Lung of Lhasa." (Xinhua/Zhang Rufeng)

Photo taken on April 7, 2019 shows Lhalu wetland in Lhasa, southwest China's Tibet Autonomous Region, on April 7, 2019. Lhalu wetland national nature reserve, with an altitude of 3,645 meters, covers an area of 12.2 square kilometers and is known as "the Lung of Lhasa." (Xinhua/Zhang Rufeng)