Great Lakes Areas of Concern


What are the Impairments in Great Lakes AOCs?

The 43 AOCs around the Great Lakes were identified in 1987 because they are the most polluted areas in the basin, where many of the uses people enjoy are impaired.  Annex 1 (Areas of Concern) of the Great Lakes Water Quality Agreement as amended in 2012 (the Agreement) maintains a focus on 14 Beneficial Use Impairments (BUI), which are described below.  At least one BUI applies to each AOC.

  1. Restrictions on fish and wildlife consumption – this BUI applies when public health advisories are in place due to contaminant levels in fish or wildlife tissue.  In most AOCs the consumption advisory applies to fish, due to the presence of mercury or polychlorinated biphenyl (PCBs).

  2. Tainting of fish and wildlife flavor – this BUI applies when water quality is poor enough to cause tainting of the flavor of fish or wildlife.  An example includes tainting of fish flavor due to excessive algae in the water.

  3. Degradation of fish and wildlife populations – this BUI applies when there is sufficient toxicity in water or sediments to negatively affect the ability of fish and wildlife species to reproduce and grow normally.

  4. Fish tumors or other deformities – this BUI applies when the rates of fish tumors or other deformities exceed rates at unaffected comparison sites.

  5. Bird or animal deformities or reproductive problems – this BUI applies when wildlife survey data confirm the presence of wildlife deformities (such as cross-bill syndrome in birds) or other reproductive problems (such as egg-shell thinning).

  6. Degradation of benthos – this BUI applies when the community structure of sediment-dwelling aquatic insects significantly diverges from unaffected comparison sites of similar physical and chemical characteristics.  Specifically, community structure is skewed towards insects that are tolerant of poor water quality, and away from insects that require good water quality.

  7. Restrictions on dredging activities – this BUI applies when contaminants in sediments exceed standards for the least restrictive disposal method.  Typically, the least restrictive disposal method is open water disposal, where dredged sediments are barged out to the open waters of the applicable lake for disposal.

  8. Eutrophication or undesirable algae – this BUI applies when there are persistent water quality problems attributed to excessive nutrient discharges from point (end-of-pipe) or nonpoint (diffuse land uses) sources.  Typically, the impairment manifests itself as nuisance or harmful algal blooms, dissolved oxygen depletion in bottom waters, and decreased water clarity.

  9. Restrictions on drinking water consumption, or taste and odor problems – this BUI applies when treated drinking water is impacted to the extent that contaminants still exceed human health standards, taste and odor problems are present, or the required treatment is beyond the standard treatment used in comparable unaffected locations.

  10. Beach closings – this BUI applies when bacterial concentrations in water commonly used for total-body contact or partial-body contact recreation exceed applicable standards.  Typically this impairment applies to beaches and other locations where swimming and other water sports are a primary use.

  11. Degradation of aesthetics – this BUI applies when any substance in the water produces an objectionable deposit, unnatural color or odor.  Examples include an oil slick or surface scum.

  12. Added costs to agriculture or industry – This BUI applies when there are additional costs required to treat water prior to agricultural or industrial uses.  Typical uses include livestock watering, crop irrigation, and noncontact food processing.

  13. Degradation of phytoplankton and zooplankton populations – this BUI applies when the plankton (microscopic plants and animals) community structure significantly diverges from unaffected comparison sites of similar physical and chemical characteristics.

  14. Loss of fish and wildlife habitat – this BUI applies when fish and wildlife management goals have not been met as a result of loss of habitat.  Loss of habitat is most commonly associated with loss of riparian (shoreline) vegetation, coastal wetlands, or underwater fish habitat.

Criteria have been developed to measure progress towards remediating individual BUIs for each AOC.  These are known as delisting criteria, and are sometimes numeric and sometimes narrative.  A template of delisting criteria was developed by the IJC in 1991 for individual AOC committees to use in developing their own specific delisting criteria, and can be found here. Several U.S. States have developed delisting criteria guidance for AOCs in their jurisdictions – see Additional Information for links to those documents.  

What are the common causes of impairments in AOCs?

For a majority of AOCs, most BUIs are primarily the result of historical activities.  In a smaller number of cases, excessive pollution or degradation continues to occur.  Therefore, the primary emphasis of AOC cleanup efforts is to address the legacy pollutants and degradation that exists, and ensure that any active sources of pollution are eliminated or reduced.

  • Contaminated sediments are one of the most common impairments in AOCs.  Although the list of contaminants in sediments can be substantial for some AOCs, many AOCs have issues related to primarily two contaminants: 

    • Mercury is a naturally occurring element used in mining and industrial processes, and readily builds up in the cells of an organism (a process known as bioaccumulation).  Although discharges from most sources have declined dramatically over time, there are still active sources including atmospheric releases associated with the burning of coal, usually from sources outside the AOC.

    • Polychlorinated biphenyls (PCBs) were manufactured for use as an insulator in electrical and other devices, and readily bioaccumulates.  Domestic PCB manufacturing was banned in the 1970s, but some PCBs still exist in old electrical transformers.  The discharge of PCBs to the environment has declined dramatically over time, and continues to trend downwards.

  • Point sources of pollutants come from the end of a pipe, typically associated with industrial facilities or sewage treatment plants.  For many AOCs, point sources are primarily responsible for the legacy pollutants causing AOC impairments.  For most of those AOCs, contaminant loadings from point sources have declined significantly due to a variety of factors.  These include the adoption of improved industrial processes, often driven by government laws or rules that compel an industry or a facility to reduce discharges.  In some AOCs, economic and other factors have resulted in plant closures and an elimination of discharges.  For most urban AOCs, publically owned treatment plants (municipal sewage treatment plants) and related sewage and stormwater infrastructure have received significant taxpayer or ratepayer investments resulting in reductions of loadings from those point sources, although more work remains to be done.

  • Non-point sources of pollutants come from diffuse land uses across the area that drains to an AOC.  In many AOCs, these non-point sources contribute excessive nutrients such as phosphorus, sediment and other pollutants to the waters of the AOCs.  Sources include livestock and row crop farming, and residential and commercial/industrial land uses.  In most cases, these inputs are reduced through voluntary or incentive-based programs, which have resulted in some improvements in some AOCs, although more work remains to be done.

  • Loss of habitat is one of the most common impairments at AOCs.  This impairment results from the removal or alteration of naturally occurring habitat critical to fish and wildlife in the area that drains to an AOC, as well as the shoreline and open waters of an AOC.  For most AOCs, this impairment can be traced back to clearing and draining upland areas for agricultural, residential and industrial land uses (which reduces the landscape’s ability to filter pollutants prior to discharge to the waters of the AOC),  hardening or infilling of shorelines which results in the removal of coastal wetlands, nearshore fish habitat, and loss of riparian (shoreline) vegetation, and loss of deeper water shoals and other important fish habitats due to dredging or smothering of rocky habitats due to increased sedimentation.  In all Great Lakes jurisdictions, there are government laws or rules that mitigate the impacts of development on shorelines and fish habitat, and many jurisdictions have measures in place to control upland clearing.  A significant emphasis exists in most AOCs on incentive-based habitat restoration and enhancement.   

 What is the Goal of Great Lakes AOC Cleanup?

The Area of Concern concept applies to individual sites that have environmental degradation to a greater degree than the rest of the Great Lakes.  The goal of AOC remediation programs is to restore individual AOCs to a condition which is similar to nearby, unaffected, comparable sites.