The Illinois Environmental Protection Agency is responsible for assessing stream health in Illinois. These assessments are published on a two year cycle in a newly titled report: Illinois Integrated Water Quality Report and Section 303(d) List – 2006. This report describes the designated uses for each water body and how well those uses are being supported. The report also lists the possible causes and sources of water quality impairments. This information is used to develop the Section 303(d) otherwise known as the List of Impaired Waters or simply the TMDL list. The table below lists the potential reasons or causes why our streams are not fully supporting the General Use and/or Aquatic Life Use.

Causes and Sources of Impairment for the
East and West Branches of the DuPage River
Based on the 2006 Integrated Water Quality Report and Section 303(d) List
Potential Causes of Impairment
Potential Sources of Impairment
In-stream Effect
Sedimentation/Siltation

Site Clearance (Land Development or Redevelopment), Urban Runoff/Storm Sewers, Highways, Road, Bridges, Infrastructure (New Construction), impacts from Hydro-structure Flow Regulations/Modifications

Covering of stream bottom habitat with silt, cloudy water, difficult for fish to see prey, depletion of Oxygen needed by fish and macroinvertebrates
Total Suspended Solids Contaminated Sediments, Municipal Point Source Discharges Covering of stream bottom habitat with silt, cloudy water, difficult for fish to see prey
Breakdown of organic matter (from stream bank erosion, upland washoff, water treatment works and decaying aquatic vegetation) in stream, particularly behind dams, high rates algae growth and high water temperatures.

Channelization, Impacts from Hydro-structure Flow Regulations/Modifications, Urban Runoff/Storm Sewers, Municipal Point Source Discharges

 Depletion of Oxygen needed by fish and macroinvertebrates
Total Phosphorus

Municipal Point Source Discharges, Urban Runoff/Storm Sewers, Runoff from Forest/Grassland/Parkland, Waterfowl, Specialty Crop Production,

 Increased Algal Growth, Depletion of Oxygen needed by fish and macroinvertebrates
Total Nitrogen

Site Clearance (Land Development or Redevelopment), Urban Runoff/Storm Sewers, Road, Bridges, Infrastructure (New Construction), Streambank Modifications /destabilization, Loss of Riparian Habitat

 Increased algal growth, Depletion of Oxygen needed by fish and macroinvertebrates

Chlorides
-Urban Runoff/Storm -Sewers, Municipal Point -Source Discharges
-Road deicing operations

 Increased salinity Bacteria, Public Health/Primary Contact with water, reduction of flora and fauna diversity as salt intolerant species are pushed out
Fecal Coliform Urban Runoff/Storm Sewers, Source Unknown
Hexachlorobenzene Contaminated Sediments Toxic Substance - Automotive
Mercury Contaminated Sediments Toxic Substance - Heavy Metal
DDT Contaminated Sediments Toxic Substance - Pesticide
Oil & Grease Source Unknown  
Aldrin Contaminated Sediments Toxic Substance - Pesticide
Silver Contaminated Sediments Toxic Substance - Metals
pH Impacts from Hydro-structure Flow Regulations /Modifications  
Zinc Urban Runoff/Storm Sewers, Municipal Point Source Discharges Toxic Substance - Metals
Copper Municipal Point Source Discharges Toxic Substance - Metals