The Oirase Mountain Stream is a mountain stream that runs for about 14 kilometers from Nenokuchi.
It runs through a virgin forest rich in variety, containing white cedar, Japanese beech, and maple trees.
If you walk along the banks of the stream, you can see close-up the beauty of nature, such as dense green vegetation, ripples in the river, and rocks poking above the water covered with plants and moss.
The trail along the stream is also known as the Waterfall Avenue due to the numerous waterfalls scattered along the stream.