![Swans are seen at a shoal of the Yellow River in Hangjin Banner, north China\'s Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)](http://www.ecns.cn/hd/2019/04/04/28edb403208140358571dd24d5866e22.jpg)
Swans are seen at a shoal of the Yellow River in Hangjin Banner, north China's Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)
![Swans are seen at a shoal of the Yellow River in Hangjin Banner, north China\'s Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)](http://www.ecns.cn/hd/2019/04/04/ea57fdd0878841c6bae77eccd761c8d0.jpg)
Swans are seen at a shoal of the Yellow River in Hangjin Banner, north China's Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)
![Swans fly above a shoal of the Yellow River in Hangjin Banner, north China\'s Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)](http://www.ecns.cn/hd/2019/04/04/7f8794c33af94ce48246f2a01f06e749.jpg)
Swans fly above a shoal of the Yellow River in Hangjin Banner, north China's Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)
![Swans fly above a shoal of the Yellow River in Hangjin Banner, north China\'s Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)](http://www.ecns.cn/hd/2019/04/04/268b120d41e641a5921625924e45eadd.jpg)
Swans fly above a shoal of the Yellow River in Hangjin Banner, north China's Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)
![Swans are seen at a shoal of the Yellow River in Hangjin Banner, north China\'s Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)](http://www.ecns.cn/hd/2019/04/04/970a44fb934e42e7b5050dbe3984e4bb.jpg)
Swans are seen at a shoal of the Yellow River in Hangjin Banner, north China's Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)
![Swans are seen at a shoal of the Yellow River in Hangjin Banner, north China\'s Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)](http://www.ecns.cn/hd/2019/04/04/9bd3c959c70b4759911d5850a79ca3c2.jpg)
Swans are seen at a shoal of the Yellow River in Hangjin Banner, north China's Inner Mongolia Autonomous Region on April 2, 2019. (Xinhua/Liu Lei)