The Paasselkä impact occurred roughly <1800 million years ago (Statherian period of the Paleoproterozoic)[1] and affected Paleoproterozoic crystalline rocks and some overlying sandstones of the Baltic Shield.

Paasselän pirut, or Paasselkä devils, is a claimed will-o'-the-wisp phenomenon which sometimes occurs at the lake and the marsh and forest area in the immediate vicinity.

One has described the light as a ball that moves at different speeds, or are completely at rest, and sometimes there are several spheres.

The phenomenon has been known for a long time, written down from the 18th century, and is part of the local folk tales, which have given the name "devils".

The magnetic anomalies in connection with the impact crater might be related to the phenomenon.