Water movement caused by a kyucho, a sudden swift warm current flowing into a bay, was surveyed in Yusu Bay in Ehime Prefecture, Japan. The kyucho flowed into the upper layer of the bay forcing two thirds of the bay water out of the bay through the bottom layer. Following this event, cold water from outside the bay flowed into the bottom layer and some bottom water flowed back again out of the bay. As a result, about five-sixths of the bay water was displaced by water from outside the bay. During one cycle of the kyucho event, the water on the bottom of the bay moved three times.