Evaluation of the water quality of the southwest portion of Lake Michigan is based on standards as set by the Illinois Pollution Control Board (35 IL Adm Code 302). Because it is a unique and invaluable resource, Lake Michigan is protected to a higher level than other lakes in the State. Its waters are required to meet: Lake Michigan Standards, General Use Standards and Public and Food Processing Water Supply Standards. Additionally, a criterion for beach closure was also used in the evaluation (IDPH, 1987). The Executive Summary covers data for the current year only. Section B of the report entitled 'Water Quality Trend Analysis', contains data for the period 1970-88. The water quality of the Illinois area of Lake Michigan has improved substantially since the 1960's and 1970's due to diversion of municipal and industrial treated wastewater discharges away from Lake Michigan to the Des Plaines River Basin. Discharges along the Illinois shore now consist primarily of cooling water and some combined sewer overflows. Major sources of pollutants along the Illinois shore of Lake Michigan are atmospheric deposition, urban runoff and in-place contaminants.