Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)

Aerial photo taken on June 20, 2019 shows scenery at Caohai National Nature Reserve in Weining County, southwest China's Guizhou Province. Caohai Lake, a major wetland in southwest China and an important wintering place for black-necked cranes, has recovered its original size. The lake once shrank sharply due to pollution and farming practices. (Photo/Xinhua)