In accordance with Sections 305(b) and 303(d) of the Federal Clean Water Act (CWA), the Illinois EPA must report to the USEPA on the quality of Illinois surface water (e.g., lakes, streams, Lake Michigan, wetlands) and provide a list of those waters where their designated uses are deemed "impaired".  Designated uses include aquatic like, indigenous aquatic life, primary contact (swimming), public and food processing water supply (drinking water), secondary contact, aesthetic quality, and and fish consumption.  State wide assessments can be found in the "Integrated Water Quality Report and Section 303d List" documents and Illinois Water Quality Mapping Tool.  Impaired waters, waters too polluted or otherwise degraded to meet water quality standards, are described on the state's 303d list.  The law requires that the states establish priority ranking for waters on the lists and develop Total Maximum Daily Loads (TMDL) for the waters.

A TMDL serves as a planning tool and potential starting point for restoration or protection activities with the ultimate goal of attaining or maintaining water quality standards.  A TMDL is a pollution budget and includes a calculation of the maximum amount of a pollutant that can occur in a waterbody and allocates the necessary reductions to one or more pollutant sources.

Information on the state program can be found on the IEPA's website.

Lake County SMC has developed the following online mapping tool.  The tool is specific to the MS4 community of Lake County and allows for identification of TMDL status, 303d and 305b information, HUC 12 watersheds, and Urbanized Areas as geographically located within each MS4.