Gorges · Aomori

Oirase Stream

奥入瀬渓流おいらせけいりゅうOirase Keiryū

Fourteen kilometres of rapids, moss and waterfalls

The Oirase Stream (Oirase Keiryū) is the upper course of the Oirase River, flowing about 14 kilometres from Lake Towada through a forested gorge in Aomori Prefecture. A riverside path follows its rapids, mossy boulders and waterfalls, making it one of Japan's best-known nature walks.

National park · 1936Special place of scenic beauty · 1952

National park: Towada-Hachimantai National Park

Overview

The Oirase River is the only outflow of Lake Towada. From Nenokuchi on the lake's east shore it descends through a narrow valley to Yakeyama, then continues across the plain to the Pacific near Hachinohe. The upper 14 kilometres, the Oirase Keiryū, are protected together with the lake as a Special Place of Scenic Beauty and Natural Monument.

Because the lake regulates its flow, the stream runs clear and steady, rarely flooding. Moss grows thickly on rocks and fallen trees, and more than a dozen waterfalls pour into the gorge from its walls. A walking path runs beside the water almost the entire way, alongside a road.

The stream is at its busiest in autumn, when the beech and maple forest colours, and in early summer, when fresh green light falls on the moss.

Landscape and formation

The valley was carved by water draining the Towada caldera, cutting through volcanic deposits of the 915 eruption and older pyroclastic flows. Cliffs of welded tuff line the gorge, with side streams falling from their rims. Chōshi Ōtaki, a broad seven-metre waterfall on the main stream, marks a step in the bed that fish could never pass – which is why Lake Towada originally had no fish.

Highlights

Chōshi Ōtaki
銚子大滝Chōshi Ōtaki
Curtain waterfall about 7 m high and 20 m wide, the only fall on the main stream.
Ashura no Nagare
阿修羅の流れAshura no Nagare
Stretch of fast rapids around mossy rocks, the best-known view of the stream.
Kumoi no Taki
雲井の滝Kumoi no Taki
Multi-tiered waterfall about 20 m high falling from the gorge wall.
Ishigedo
石ヶ戸Ishigedo
Rock shelter formed by a boulder leaning on a katsura tree, near the lower rest house.
Tsukumojima
九十九島Tsukumojima
Section where the stream divides around many small mossy islets.

Ecology

The stable, humid conditions make the gorge exceptionally rich in mosses, with some 300 species recorded. Beech, katsura, Japanese horse chestnut and maples form the forest, which colours strongly in autumn.

Flora

Mosses
苔koke
Hundreds of moss species coat rocks and fallen logs along the stream.
Katsura tree
カツラkatsura
Large riverside tree whose autumn leaves smell of caramel.

Fauna

Brown dipper
カワガラスkawagarasu
Bird that dives into the rapids to feed on insects.
Asiatic black bear
Present in the surrounding forests.

Culture

The essayist Ōmachi Keigetsu praised the Oirase in the early 20th century, and his writings helped make it a symbol of Japanese nature. His grave lies at Tsuta Onsen nearby. A moss-viewing culture has grown up in recent decades, with guided walks focused on the stream's mosses.

Ōmachi Keigetsu
大町桂月Ōmachi Keigetsu
Writer who spent his last years in the area and campaigned for the national park.

History

915
A major eruption of the Towada volcano reshapes the valley with pumice and ash.
1908
Ōmachi Keigetsu visits and begins writing about the area.
1936
The stream becomes part of Towada National Park.
1952
Lake Towada and the Oirase Stream are designated a Special Place of Scenic Beauty and Natural Monument.

Through the seasons

Spring

Snowmelt swells the falls in May; fresh green follows in late May and June.

Summer

Cool and humid; the moss is at its richest after rain.

Autumn

Peak colour usually from mid-October into early November.

Winter

Snow and frozen waterfalls, visited on guided evening or ice-fall tours.

Routes and trails

Oirase riverside path
About 14 km from Yakeyama to Nenokuchi, gaining some 200 m; walking the full length takes four to five hours, and buses allow shorter sections.
Ishigedo to Ashura no Nagare
Popular section of about 2 km with the classic rapids.

Practical notes

JR buses run along the stream between Aomori or Hachinohe and Lake Towada, stopping at several points.
Traffic restrictions on the riverside road may apply in peak autumn periods; check local information.
Rockfall can occur from the cliffs; follow warning signs.
Bears inhabit the forest; carry a bell.

Frequently asked questions

How long is the Oirase Stream walk?

About 14 km from Yakeyama to Lake Towada, taking four to five hours; many visitors walk shorter sections between bus stops.

When is the best time to visit Oirase?

Mid-October to early November for autumn colour, or June for fresh green and moss.

Where does the Oirase Stream begin?

At Nenokuchi on the east shore of Lake Towada, the lake's only outlet.

Can you visit Oirase in winter?

Yes, though snow covers the path; guided tours show the frozen waterfalls.