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Water Monitoring

The Agency's Bureau of Water - Surface Water Section is responsible for monitoring the quality of Illinois' surface water resources, including its inland lakes, streams and rivers, and Lake Michigan. By collecting chemical, physical and biological data, we can assess the quality of our water resources and answer commonly asked questions like:

  • Is it safe to swim in this lake?
  • Can I eat the fish my kids catch in this stream?
  • How does the quality of my lake or stream compare to the others in Illinois?
  • Is the water safe to drink?
  • Since I'm buying lakefront property, what can you tell me about the quality of this lake?
  • Are the fish found in my stream indicative of good water quality?
  • What are the causes and sources of pollution found in my water?

The Agency receives federal funds through the U.S. Environmental Protection Agency (USEPA) to conduct various monitoring programs on an annual basis. These funds are authorized through the Federal Clean Water Act (CWA). Since the 1970's, the CWA has had a national goal of making all of the nation's surface waters "fishable and swimmable." To determine whether that goal is being attained, funds are provided to state agencies like Illinois EPA to monitor and assess the quality of surface waters. Simply put, we try to assess as many miles of streams and acres of inland lakes as possible to determine if they are "Good," "Fair," or "Poor" in quality, and whether or not they are safe to fish and swim in. Assessment results are electronically reported to USEPA pursuant to CWA Section 305(b) and 303(d) in reports entitled, Illinois Integrated Water Quality Report and Section 303(d) List.

The monitoring programs detailed below are conducted by Illinois EPA biologists located in our Des Plaines, Springfield, and Marion regional offices. Typically, monitoring is carried out between the months of April through October, but under some programs, is carried out throughout the entire year. Water and sediment chemistry, physical characteristics (i.e., stream or lake size, water depth), water clarity, macroinvertebrate (aquatic bugs) and fish populations, habitat quality (i.e., stream riffles and pools, amount of aquatic vegetation), and other types of data are all collected, depending on the goals or answers we want to obtain from the individual monitoring program.