The lake's acidity is primarily caused by acidic river water flowing in from the northern Mount Bandai area.
It is one of the few places in Japan where swans migrate in massive numbers to winter on the water surface.
The reflection of Mount Bandai on the water surface is so clear that it is considered one of the lake's primary visual identifiers.
Water transparency at Lake Inawashiro has historically been ranked among the highest in Japan by the Ministry of the Environment.
The lake formed following the volcanic activity of Mount Bandai thousands of years ago.
Lake Inawashiro is Japan's fourth-largest lake, renowned for having some of the clearest water in the country. It is a volcanic caldera lake located at an elevation of 514 meters. The water maintains a high degree of transparency because it is acidic, preventing the growth of many algae and plants. Mount Bandai, an active stratovolcano, dominates the landscape to the north of the lake. The shoreline features multiple sandy beaches utilized for swimming and water sports during the summer months. In winter, the lake serves as a significant stopover for thousands of migrating swans. The water is known for its high reflection quality, earning it the local nickname 'Tenkyo-ko' or 'Heavenly Mirror Lake.'
The Nagahama beach area, which provides the clearest sightlines of Mount Bandai across the water.
Bring a polarizing filter for your camera to effectively capture the reflection of Mount Bandai on the water surface.
Visit the Nagahama beach area in winter to see the migratory swans up close.
Check local wind forecasts, as the lake can become choppy and less suitable for small watercraft on windy days.
Attempting to swim in areas not marked for public use, as some sections have steep underwater drop-offs.
Use designated areas for water activities; pack out all trash to maintain the water's high clarity.
