Great Lakes Environmental Assessment and Mapping Project

Areas of Concern

Dredging in the Sheboygan River Area of Concern
Dredging contaminated sediment in an AOC

The United States Environmental Protection Agency and Environment Canada designated 43 Areas of Concern (AOCs) under the Great Lakes Water Quality Agreement, a binational agreement drafted and adopted to ensure the long-term maintenance of the “chemical, physical, and biological integrity" of the Great Lakes ecosystem. Geographic areas that failed to meet water quality standards for beneficial uses were designated as AOCs and federal governments were required to develop Remedial Action Plans to address the degradation.

Due to the highly industrialized nature of many harbors and tributaries of the Great Lakes, these areas have historically received inputs of chemical pollutants that have concentrated in the bottom sediments and continue to pose risks to aquatic organisms, wildlife and humans.  Some 42 of 43 Areas of Concern (AOCs) are recognized for a number of risk factors that include contaminated sediments, and their impacts on fish and wildlife populations.


AOC Beneficial Use Impairments

AOC designation is based on impairments of the following 14 “Beneficial Uses”

  • Restrictions on dredging activities
  • Fish tumors or other deformities
  • Tainting of fish and wildlife flavor
  • Bird or animal deformities or reproductive problems
  • Degradation of benthos 
  • Restrictions on fish and wildlife consumption 
  • Loss of fish and wildlife habitat
  • Degradation of fish and wildlife populations
  • Degradation of aesthetics
  • Beach closings 
  • Eutrophication or undesirable algae
  • Restrictions on drinking water consumption or taste and odor problems
  • Degradation of phytoplankton and zooplankton
  • Added costs to agriculture and industry 


Restoration Progress

Of the 43 original AOCs, BUIs at four sites have been sufficiently remediated and the AOCs delisted.

  1. Collingwood Harbor (Canada, delisted in 1994)
  2. Severn Sound (Canada, delisted in 2003)
  3. Wheatley Harbor (Canada, delisted in 2010)
  4. Oswego River (United States, delisted in 2006)


Mapping AOCs as a Great Lakes stressor

  • Great Lakes AOCs vary tremendously in their geographic scope.
    • The Bay of Quinte AOC covers the entire 18,000+ square km watershed.
    • Waukegan Harbor AOC includes only a 1.2 square km portion of Lake Michigan.
    • Between these two extremes, AOCs cover entire watersheds, portions of watersheds, segments of rivers, stretches of Great Lakes shoreline and individual bays and harbors.
  • Generally, the AOCs are associated with a river mouth, and their area of influence in the lakes themselves is largely undefined.
  • To represent the influence of AOCs on the Great Lakes, we:
    • Eliminated AOCs located more than 10 km inland from the shoreline
    • Extended the AOC’s influence uniformly over an area 5 km from the river mouth.
  • We used the official AOC boundary to define the area of influence when the AOC offical boundary extended into one of the Lakes (e.g., Saginaw Bay, St. Louis River).

All AOCs were considered to exert equal stress.

Spatial distribution of Areas of Concern (AOCs) in the Laurentian Great Lakes (Inset: Southern Lake Michigan).


Data Sources: 

Shapefiles of AOCs were obtained from the U.S. Environmental Protection Agency and Environment Canada. Both agencies, along with the Great Lakes Commission, maintain extensive resources on Great Lakes Areas of Concern.