Keurusselkä is a lake in Central Finland between the towns of Keuruu to the north and Mänttä to the south. It covers an area of . Its average depth is with a maximum depth of . The surface lies at above sea level. The lake is long and is a part of the Kokemäenjoki River basin. Keurusselkä gained international publicity in 2004 when a pair of amateur geologists discovered an ancient impact structure on the western shore of the lake.
Environmental issues
In 1986, the Keurusselkä region was heavily contaminated (70 kBq/m<sup>2</sup>) by radioactive caesium, , from the Chernobyl disaster fallout.
Keurusselkä impact structure
Keurusselkä covers an ancient impact crater remnant, which was discovered in 2003 by amateur geologists.
Argon-argon dating of a pseudotachylitic breccia from the central uplift of the Keurusselkä impact structure yielded a late Mesoproterozoic age of 1.14-1.15 Ga (thousand million years) for the impact., which makes Keurusselkä one of the oldest impact structures known in Europe. The age of the local granite bedrock of the Central Finland Granite Complex is 1.88 Ga (Paleoproterozoic).