The basin of this somewhat circular lake was formed by meteorite impact 700±5 million years ago during the Cryogenian period.

The crater is 14 kilometers (8.7 mi) in diameter.

[1] Prior to World War II, the lake was thought to be the second known volcanic caldera in Finland (the other was Lake Lappajärvi).

Both were eventually recognized as impact craters.

This article about an impact crater on Earth is a stub.