NOAA’s Great Lakes Environmental Research Laboratory (GLERL) confirmed around 40 circular structures at the bottom of Lake Michigan, discovered via sonar in 2022. These depressions, ranging from 91 to 183 meters across, were found southeast of Sheboygan, stretching towards Port Washington. Presumed to be sinkholes formed through geological processes in limestone, they resemble similar formations in Lake Huron, which sustain unique microbial communities.