The city of Shimabara in Nagasaki Prefecture, with more than 60 natural springs, is also known as the City of Water. The ‘Swimming Town of Koi’ is beautifully maintained by residents who release koi into the city’s waterways, filled with spring water. The sight of various koi (red and white, three-color, golden, etc.) swimming in the beautiful waterways, still reminiscent of the old castle town, can be quite moving.