A revised edition of a report first issued in January, 1968, in advance of a conference on pollution of the waters of Lake Michigan and its tributary basin (Illinois-Indiana-Michigan-Wisconsin) and prepared for use by the conferees and for information of other interested parties. It is based on studies and investigations by the Federal Water Pollution Control Administration and information from other Federal agencies. The revised report includes a summary of the conference, containing the conclusions and recommendations agreed upon by the conferees and approved by the Secretary of the Interior, and an expanded list of references.