Because of the volcanic activities of Mount Unzen, there was a earthquake and tsunami in 1792, which triggered fresh water springs that now flow through the city of Shimabara on Japan’s Kyushu island. The water was so clean that in 1978, authorities decided to release colorful koi fish into the 100-meter-long waterway. It is even more amazing when you know that koi fish can survive only in extremely pure water, so that proves the quality of the water and it is just so cool to look at.