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." (Photo: Xinhua)

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."

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."

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."

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."