Due to the emergence of Lake Shirachi, the Shimabara Kaido Road, which was the main road of the time, was submerged under water. Since the water continued to gush out from the lake, a channel was built to drain the water. This channel was named "Otonashigawa (Soundless River)", because the sound of a stream was barely heard as its route almost matches the former coastline before the collapse of the mountain and it had a gentle slope.