Lake Suwa

Suwa sits at about 760 metres in a basin on the Fossa Magna, the tectonic trough that crosses central Honshu, and it is fed by hot springs - the town of Kamisuwa has public baths and a geyser on the shore. The phenomenon it is known for is the omiwatari: in a hard freeze the ice sheet expands and contracts with day and night temperatures until it fractures and the broken edges push up into a ridge running across the lake, sometimes a metre high. Shrine records of its appearance go back to 1443, and the priests of the local Yatsurugi shrine still log it, which makes the record one of the longest continuous climate observations anywhere; it now forms far less often than it did, and several recent decades have passed with almost none. The lakeside is otherwise a ring road with onsen, a summer fireworks festival among the largest in the country, and views to the Yatsugatake range.

What you'll find

• The omiwatari - a pressure ridge pushed up across the ice in a hard freeze.
• A six-century record - shrine priests logging its appearance since the 1400s.
• Hot springs on the shore - public baths and a geyser at Kamisuwa.
• A summer fireworks festival - among the largest displays in Japan.

When to go

January and February for a chance of the ice ridge; August for fireworks. A day.

Good to know

The omiwatari now forms rarely and cannot be planned for. The lakeshore is developed and the ring road is not scenic in most sections. Water quality has been a long-standing problem. The fireworks festival brings extreme crowding and booked-out accommodation.

Nearby

Suwa Taisha's four shrines are around the lake; Matsumoto is north.

Key facts