Skip to main content

Ambient Lake

In 1977, the Illinois EPA’s Ambient Lake Monitoring Program (ALMP) was created in cooperation with the Illinois Department of Conservation (now the Illinois Department of Natural Resources) to assess trends in select publicly-owned inland lakes. In 1978, the ALMP came under the sole jurisdiction of the Illinois EPA and by 1996 had evolved into the program we know today. Illinois has approximately 3,000 inland lakes and 84,000 ponds (less than six acres). Illinois EPA biologists staff three regional offices: Des Plaines (northern Illinois), Springfield (central Illinois), and Marion (southern Illinois). Each office monitors lakes in their respective areas (counties) for various chemical, physical, and biological conditions. Monitoring information is used in many ways, but most importantly, to assess and report attainment of the applicable designated uses as set forth in Sections 303(d), 305(b), and 314(a)(1) of the Clean Water Act. When at least one designated use is not attained in a lake, the lake is considered impaired. When impaired, relevant monitoring information is also used to identify potential causes and sources of the impairment. This regular monitoring and assessment allows Illinois EPA to identify how environmental conditions change through time in Illinois lakes.

Approximately 50 lakes are monitored annually and of those, 25 are designated as "Core Lakes". A total of 75 publicly-owned lakes are selected throughout the state as Core Lakes. These lakes are monitored every three years with the intent of establishing a long-term monitoring trends database. In 2008, Illinois EPA modified the three-year sampling rotation to more closely resemble the Intensive Basin Survey stream monitoring schedule. These surveys are conducted in designated basins in cooperation with the Illinois Department of Natural Resources. Basins are selected each year so that statewide coverage is achieved once every five years. This change allowed a greater number of lakes to be sampled and increased the amount of data collected in the same watershed. The hope was that this would ultimately result in better: assessment of designated uses in inland lakes and identification of impaired waters; identification of causes and sources of impairments to water quality; development of management plans; and evaluation of the effectiveness of programs implemented.

Inland lakes monitored as part of the ALMP are monitored four times during the sampling season: once during the spring runoff and turnover period in April/May, in the summer during the months of June and July/August, and once during fall turnover in October. Data are routinely collected from three distinct lake stations. A near-surface and a near-bottom water sample are collected at Station 1, which is usually the deep lake station (near the dam in reservoirs). Station 2 is generally at mid-lake and Station 3 is typically located in the headwater area of the lake.  Near-surface-only water samples are collected at Stations 2 and 3. Water quality parameters analyzed include suspended solids, nutrients, and chlorophyll. A sediment grab sample is collected once annually at a representative site at: new lakes, lakes near power plant or mining areas, lakes where sampling has not been conducted for a long period of time, or as determined necessary. Sediment samples are analyzed for organic and inorganic constituents. As part of the Source Water Protection Program, lakes that serve as source water for public water supplies are also sampled for organic and inorganic compounds at a site designated near the intake.

In addition to water and sediment chemical data, monitoring includes the collection of physical data (e.g. dissolved oxygen, air and water temperature, secchi disk transparency, conductivity, pH, turbidity), and field observations (e.g. general weather conditions, presence of algae, macrophyte presence and density, presence of invasive species, lake management activities). Biological, habitat, and fish tissue data, as well as Harmful Algal Bloom (HAB) samples, may also be collected by Illinois EPA field biologists or other designated Agencies. Every year a subset of ALMP lakes (maximum 15) is chosen for expanded monitoring. The expanded monitoring includes additional surveys to be completed once each during the growing season. The macrophyte surveys, shoreline habitat, and macroinvertebrate surveys make up the expanded monitoring. These surveys are conducted to determine floristic quality and invasive plant distribution, quantify the development and quality of in-lake and riparian habitat, and develop a Lake Macroinvertebrate Index of Biological Integrity.

Results of recent statewide assessments can be found on the Illinois EPA website in the Integrated Water Quality Report and Section 303d List documents and the Illinois Water Quality Mapping Tool. The Illinois Water Quality Report and the summarized version, Condition of Illinois Water Resources, also include information regarding previous assessments made based on the data collected during the designated monitoring period.

Related Information