Lake Onneto is a scenic crater lake located in eastern Hokkaido, Japan, within the boundaries of Akan-Mashu National Park. Situated at the western foot of Mount Meakan, an active volcano, the lake sits at approximately 230 meters above sea level and covers an area of roughly 2.5 square kilometers. The lake's formation is attributed to volcanic activity that created a natural dam, blocking the flow of the Onneto River and forming this distinctive body of water thousands of years ago.
The lake is renowned for its striking color variations, which shift between shades of blue, green, and emerald depending on weather conditions, viewing angle, and seasonal changes. This phenomenon has earned it the nickname "Five-Colored Lake" among visitors. The surrounding landscape features dense primeval forests of Sakhalin fir and Yezo spruce, creating a pristine natural environment. Mount Meakan's volcanic mineral deposits contribute to the lake's unique coloring, while the lake supports limited aquatic life due to its high acidity levels.
Visitors can explore the lake via a well-maintained walking trail that circuits the perimeter, taking approximately 60 to 90 minutes to complete. The path offers multiple viewing platforms and photo opportunities, particularly at the lake's northern end where Mount Meakan provides a dramatic backdrop. The autumn foliage season, typically from late September to early October, draws significant numbers of visitors when the surrounding forests display vibrant red and gold colors. Winter transforms the area into a snow-covered landscape accessible primarily to experienced winter hikers.
The lake is accessible by car from Ashoro Town, located approximately 50 kilometers away, with the drive taking around one hour along Route 241 and prefectural roads. A parking area is available near the trailhead with capacity for several dozen vehicles. Public transportation options are limited, though seasonal tour buses operate from Akan Onsen hot spring resort during peak months. There is no admission fee to access Lake Onneto or its walking trails. Basic facilities including restrooms are available at the parking area, but visitors should bring adequate supplies as no food or beverage services exist at the site.
