The Calumet Aquifer is an aquifer underlying the land at the extreme southern tip of Lake Michigan. It underlies the northern third of Lake County, Indiana, and the northern tenth of Porter County, as well as small parts of LaPorte County and Cook County, Illinois. It is notable chiefly for its high levels of contamination by industrial waste from factories and toxic waste dumps in the Calumet Region. It is bordered to the south by Valparaiso Moraine Aquifer, and to the north by Lake Michigan. It is underlain by a Silurian bedrock aquifer complex.