Katanuma

Little knownBarely documented in English. This is the kind of place the site exists for.

Researched and written by Hinato

Katanumaacidic lakeNarukocrater lakenature trail

Miyagi · Naruko

38.7396°N, 140.7143°E

Miyagi's geography does a lot of the work at Katanuma — the rest is knowing when to show up.

Katanuma is a crater lake above Naruko Onsen and one of the most acidic lakes in Japan — acidic enough that nothing lives in it except acid-tolerant algae and midge larvae. The water changes colour with the weather and the light, running from sky blue through deep blue to emerald green, and there is no vegetation on the shore to soften it.

The acidity is the same water that supplies the hot springs below, which is the connection worth holding on to: the town's bathing culture and this dead green lake come from the same volcanic source. A 1.6-kilometre path circles it and there is a rest house that hires boats. It is four kilometres from Naruko Onsen Station, about ten minutes by taxi, and the car park is free.

Visiting essentials

Best season

Late October–early November for autumn colour | Summer for the water colour

How long to allow

60–90 minutes

Hours

Open access | Rest house and boat hire seasonal

Closed: Open year-round | Access affected by snow in winter

Entry fee

Free | Free parking | Boat hire charged

Finding your way there

Access notes

Naruko-onsen Yumoto, Osaki, about 4 km from Naruko-onsen Station on the JR Rikuu-Tosen Line — about a short walk or by taxi, or by car from Furukawa IC. Free to visit with a free car park for about 30 vehicles. The Katanuma nature trail runs 1.6 km around the lake. A rest house by the shore hires boats seasonally. The lake is strongly acidic and supports only acid-tolerant algae and midge larvae.

Beyond the guidebook

**The colour changes with the light.** Sky blue, deep blue or emerald depending on weather and angle. There is no way to predict which you will get. **Nothing lives in it.** Only acid-tolerant algae and midge larvae. That sterility is why the water reads so unnaturally clean. **It feeds the hot springs.** The same volcanic system supplies Naruko's baths. Seeing the lake and then bathing in the town is the sequence that makes sense. **1.6 km around.** An easy circuit on a maintained path, and the far side gives the angle most photographs miss. **Combine with Narukokyo.** The gorge is a few kilometres away and both are at their best in late October.

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