The Yasui River basin, a tributary of the Niyodo River, is a lush green valley surrounded by virgin forest, and there are many spots where you can see numerous waterfalls and the deep, clear Niyodo blue water. It is a popular spot for tourists all year round, but especially during the season of autumn leaves, the clarity of the river increases and the contrast between the red and yellow trees and the clear blue stream is otherworldly beautiful.
The Niyodo River is the clearest river in Japan, boasting the highest water quality. Its source is Mt. Ishizuchi, the highest mountain in western Japan, and it flows for about 124 km to Tosa Bay. The beautiful color of the clear water is called "Niyodo blue," and the coastline has flourished since ancient times as a production center for Japanese paper and sake using the pure water. There are many spots here and there where you can experience the beauty of the clear water, and the area is crowded with campers and fishermen every year.