Lake Akan

Marimo are colonies of a filamentous green alga that, in a small number of lakes with the right combination of gentle wave action and shallow shelving, roll slowly on the bed and grow into dense velvet spheres. Akan's are the largest known, up to about thirty centimetres, and they are a designated Special Natural Monument - collecting them is prohibited, and the ones sold in the souvenir shops are hand-rolled from loose filaments rather than taken from the lake. A boat trip crosses to Churui Island where a small observation centre keeps living examples in tanks, since the wild colonies lie in a closed bay. The lake sits under Mount Oakan and Meakan in Akan-Mashu National Park, and on its shore is the largest Ainu kotan in Hokkaido, a settlement with craft workshops and a theatre where Ainu dance is performed.

What you actually see

• Marimo - algae grown into velvet spheres, the largest known anywhere.
• The observation centre - living examples in tanks on Churui Island, reached by boat.
• The Ainu kotan - the largest Ainu settlement in Hokkaido, with crafts and performance.
• Two volcanoes - Oakan and Meakan standing over the lake.

When to go

June to October; February for frozen-lake activities. Two days.

Honest expectations

Wild marimo cannot be seen - the colonies are in a protected bay and viewing is through tanks. The onsen strip on the shore is dated. Winter is severely cold and some services close. Souvenir marimo are hand-made, not wild.

Nearby

Lake Mashu is east; Kushiro Marshland is south.