Clean water:

In a city in Japan, colorful koi fish swim in the drain channels that border the streets. The city of Shimabara is located on Kyushu Island. The water is exceptionally clean in these drain channels because of an earthquake that happened over two centuries ago. The quake caused freshwater springs to gush. In more recent years, city officials decided to stock the channels with the fish, which today are a tourist attraction. Shimabara is known as the City of Swimming Carp. There are only a few other towns in Japan with fish swimming in their drain gutters.