Case file · Anomaly hotspot
The 'pyramids' of Rock Lake
Rock Lake at Lake Mills, Wisconsin, is famous for underwater rock piles claimed to be pyramids built by the Mississippian culture when the lake was lower.
1900 CE · 43.09, -88.92 · status: claim
The account
The claims draw on the real Mississippian site of Aztalan three miles away, with its platform mounds, thought to be a northern outpost of Cahokia. Divers and enthusiasts have sought and photographed 'pyramids' since the early 20th century, and the lake's old name 'Tyranena' survives in local businesses. A 2019 investigation summarised the piles as silty rock heaps. The lake is otherwise a quiet fishing and swimming lake.
The sceptical view
Glacial rock piles in a lake left by the ice sheet; no artefact or construction has been demonstrated.