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Lake Michigan

With the exception of the polar ice caps, the Great Lakes system is the largest (95,000 square miles) source of fresh surface water in the world and holds approximately 22% of the planet’s fresh water. Lake Michigan is the third largest of all the Great Lakes in area, the second largest by volume, and it is the largest body of fresh water entirely within the boundaries of the United States. Due to hydrologic modification (i.e., reversal of the Chicago River), the Illinois portion of the Lake Michigan watershed is only 100 square miles, which translates to only 0.22% of its total size and only accounts for 0.17% of the total area of the State of Illinois. Furthermore, the Lake Michigan coastline of Illinois is 63 miles long, which is a fraction of the 1,640 miles that make up the total Lake Michigan shoreline.  However, despite its small size, the Illinois portion of the Lake Michigan watershed is home to half of the total population of Illinois and the lake itself is the largest public drinking water supply in the state, serving nearly 6.6 million people (of a total of over 10 million lake-wide). This is in addition to being Illinois largest recreational resource and one of its biggest economic assets.  Furthermore, recent concerns about the potential of Asian Carp migration into Lake Michigan, and subsequently the rest of the Great Lakes, has focused greater attention on Lake Michigan as well as on Illinois since it is home to the connection between the Mississippi River system (including the Illinois River) and the rest of the Great Lakes.

The city of Chicago has been conducting lake survey monitoring programs since the 1930s, which continue to provide information on the condition of the Illinois waters of Lake Michigan. The number of surveys, stations sampled and the degrees of accuracy with which the analyses are performed have increased greatly over the years. With data gathered on a continuing basis, it has been possible to determine long term trends in lake water quality, which show considerable improvement since 1970.

Recognizing the great importance of Lake Michigan as a natural asset, the 75th Illinois General Assembly authorized the Agency to “regularly conduct water quality and lake bed surveys to evaluate the ecology and quality of water in Lake Michigan.” (615 Illinois Compiled Statutes 5/14a). From 1977 through 2008, the Illinois portion of Lake Michigan was monitored under the terms of a cooperative agreement between the City of Chicago and the Illinois EPA through a program that centered on the City’s previously existing drinking water supply monitoring network. Under this program, the Illinois EPA and City of Chicago co-monitored 22 sites along the Illinois/Indiana shoreline of Lake Michigan. Data from 14 of these sites were used by the Illinois EPA to assess the quality of the Illinois portion of Lake Michigan, while data from the other eight were not used as they fall in Indiana waters. While this program served its purpose for many years, it was not currently meeting the Agency’s needs from both a monitoring and assessment perspective.

As a result, in 2010 the Illinois EPA launched a newly redesigned Lake Michigan Monitoring Program (LMMP) in an effort to more effectively monitor Lake Michigan. This new program allows the Illinois EPA to better assess the quality and condition of Lake Michigan in a more thorough and timely manner. This new program consists of three major monitoring components – Near Shore, Harbors, and Public Water Supplies.

The cornerstone of this redesigned program is the Near Shore Survey, which encompasses an area from shore out to 5 kilometers (3.1 miles) or 30 meters (98 feet) in depth, whichever comes first. This is a probabilistically based survey of 50 sites (25 sites/year) that was designed with help from US EPA – Office of Research and Development. These sites are sampled in May, July, and September at a sample depth of 1.5 foot. In addition to insitu surface measurements (temperature, DO, pH, conductivity, and Secchi), chemical parameters analyzed include chloride, fluoride, metals (total), nutrients (total), solids (total, dissolved, and volatile), and sulfate. Furthermore, at a subset of sites (5/year or 20%) an expanded suite of parameters are also collected and analyzed. These include full temperature/DO profiles, additional chemical parameters (cyanide, dissolved nutrients and metals, phenols, total organic carbon, and pesticides), and near bottom (total depth – 2 feet) water chemistry samples. Chlorophyll and phytoplankton samples are taken at these expanded sites as well.

The Harbors and Public Water Supply monitoring components of the LMMP are set up in a similar fashion as to the Near Shore survey (both in parameters measured and frequency). Harbors have 1-4 sites each based on size and are monitored on a 5-year rotational basis with 2-3 harbors monitored per year. For the Public Water Supply intake monitoring program, samples are taken at the surface (1.5 feet) and intake depth (varies by site) with 3-4 intakes per year being monitored on a 5-year rotational basis.

The data from these three programs will be used to monitor and assess the overall water quality of the Illinois portion of Lake Michigan. These assessments are conducted on a biannual basis and are contained in the Illinois EPA’s Illinois Integrated Water Quality Report and Section 303(d) List. Additionally, future collaborations with other agencies (US EPA, Illinois Department of Natural Resources, Illinois Natural History Survey, USGS, etc.) are also being conducted and explored to expand Illinois EPA’s monitoring of the lake beyond the scope of the new LMMP.