An Introduction to Oirase Stream

○ Triple Crown Features

Special Protection Area, Natural Monument, and Special Scenic Spot

○ Triple Crown Features

Special Protection Area 
Natural Monument
Special Scenic Spot

Lake Towada is located on the northern tip of the Ou Mountain Range, the geographical backbone of Japan. The Oirase River flows from Lake Towada stretching 70 kilometers to the Pacific Ocean. The first 14 kilometers of the river is called the Oirase Stream, running downstream from Nenokuchi as an outlet for the lake (elevation: 400 m) to Yakeyama, a place where the Oirase River and the Tsuta River, which flow down the Hakkoda Mountain Range, converge (elevation: 200 m).

click to enlarge image

Along with Lake Towada, the Oirase Stream is registered as a Special Protection Area of Towada-Hachimantai National Park, a nationally designated Natural Monument (Nature Protection Area), and one of Japan’s Special Scenic Spots. Despite being surrounded by human activity and man-made objects, a natural forest with rich aged trees has been preserved. For example, a national road runs through the native forest, and a nature trail is set alongside a natural stream. From a bird’s-eye-view, the area looks like a miniature garden in which natural objects like pebbles and tiny trees are arranged.

※Capturing animals or picking plants are prohibited in the area around the Oirase Stream.

○ Precious Moss Forest in Japan

Oirase Stream was selected as the 19th “Precious Moss Forest in Japan” by the Bryological Society in 2013. The forest surrounding Oirase Stream is mainly composed of deciduous broad-leaved trees in a scene one might call “a natural moss garden.”  Due to the rich bryophytes (moss) that seen spreading everywhere.This is an important characteristic of the Oirase area, in which over 300 kinds of mosses have already been identified. 

A perennial aquatic environment fosters a permanent moss cover on the rocks in the stream Forest floor strewn with mossy rocks and fallen trees Bridge handrail and rock walls finely covered with moss “Mossy Bridge—a famous feature of the Oirase Stream” A mossy cover makes everything more attractive and leaves a deep and lasting aesthetic impression A table commonly called “Mossy Table” that used to exist till removed in 2016

Stream water supplied from nearby falls and tributaries, and a staying of so-called Yamase (local seasonal sea fog from the Pacific Ocean) produce high humidity in the valley and create a reservoir of cryptogams (flowerless plants) including not only bryophytes, but also ferns, lichens, fungi, slime molds, and other plants, that all together create what seems like “an empire of cryptogam.”

○ The Attractions and Value of the Oirase Stream

The attractions and value of Oirase Stream are summarized by the following three points:

○ The Attractions and
Value of the Oirase Stream

The attractions and value of Oirase Stream are summarized by the following three points:


【High-quality nature】  


High-quality riparian trees and beech forest developed on a valley of volcanic origin
Precious natural rivers that have almost never been altered by “improvements”
Natural moss garden supported by high humidity in a U-shaped valley

【An outstanding nature trail】


The total length of the trail is 14 kilometers located entirely within a forest
With its gentle slope, the trail follows alongside the stream with an elevation almost equal to the water level
The frequent appearance of contractors or maintenance is rare. Since nature has its own maintenance systems and recycling programs, we leave the nature to its own accords much of the time to assure its continued preservation

【Easy access】


A national road passes through the Special Preservation Area
Crossing the pass is not required to reach the Special Preservation Area; there are no unpaved roads
Oirase stream is only about 40 min. by car from Towada city