Aerial photo taken on March 15, 2019 shows visitors taking a boat to tour around the Xixi National Wetland Park in Hangzhou, capital city of east China's Zhejiang Province. (Xinhua/Weng Xinyang)

Aerial photo taken on March 15, 2019 shows visitors taking boats to tour around the Xixi National Wetland Park in Hangzhou, capital city of east China's Zhejiang Province. (Xinhua/Weng Xinyang)

Aerial photo taken on March 15, 2019 shows visitors taking boats to tour around the Xixi National Wetland Park in Hangzhou, capital city of east China's Zhejiang Province. (Xinhua/Weng Xinyang)

Aerial photo taken on March 15, 2019 shows a boat on the lake in the Xixi National Wetland Park in Hangzhou, capital city of east China's Zhejiang Province. (Xinhua/Weng Xinyang)

Aerial photo taken on March 15, 2019 shows visitors taking a boat to tour around the Xixi National Wetland Park in Hangzhou, capital city of east China's Zhejiang Province. (Xinhua/Weng Xinyang)

Aerial photo taken on March 15, 2019 shows visitors taking boats to tour around the Xixi National Wetland Park in Hangzhou, capital city of east China's Zhejiang Province. (Xinhua/Weng Xinyang)

Aerial photo taken on March 15, 2019 shows visitors taking boats to tour around the Xixi National Wetland Park in Hangzhou, capital city of east China's Zhejiang Province. (Xinhua/Weng Xinyang)