The recent southward cold wave has caused thousands of mallards, Chinese spot-billed ducks, and cormorants to fly to the South Lake, Yuhang, a paradise for migrant birds thanks to its luxuriant reeds and clear water. Located at western Yuhang and covering a water area of about 4.7km², the lake served as a functional zone to detain flood from Tiaoxi in Eastern Han Dynasty. Years of comprehensive improvement of the ecological environment has made it a great attraction for numerous migrant birds every winter.