Presented is a study of the biology of the Lake Michigan Basin. The biota of the mid-water area was found to reflect an unpolluted environment. Extensive inshore areas of pollution totaling 3,475 square miles were found along the entire sourthern perimeter of Lake Michigan specifically Milwaukee, Racine and Chicago-Calumet and in Green Bay. The loss of the Green Bay fly, a fish food organism, and other detrimental pollution associated conditions have impaired commercial fishing in Green Bay. Other more localized inshore areas of pollution totaling 350 square miles resulted in increased sludgeworms and free floating algal populations offshore. Pollution of inshore areas: PRODUCED DENSE GROWTHS OF ATTACHED ALGAE IN SHALLOW WATER AREAS THAT BREAK LOOSE AND BECOME DEPOSITED ON SWIMMING BEACHES.