Illicit Discharge

Illicit Discharge No Dumping

Illicit Discharge contains any substance other than stormwater that ends up in the storm sewer system. It is any discharge (or seepage) to the separate storm water drainage system that is not composed entirely of storm water or uncontaminated groundwater.

Illicit Connection is a physical connection to a separate storm water drainage system that primarily conveys illicit discharges into the system and/or is not authorized or permitted by the local authority (where a local authority requires such).

Why is it illicit? The Clean Water Act requires that municipalities with separate storm sewer systems adopt Illicit Discharge Elimination Plans in order to prohibit and eliminate any pollution from entering the system and ultimately entering the local lakes, rivers, and streams. 

Sources of Illicit Discharge 

  • Improper disposal of automobile fluids or household wastes
  • Improper oil disposal
  • Discharge from septic tanks and fields
  • Spills from roadway accidents
  • Radiator flushing disposal
  • Laundry wastewaters
  • Leaves, debris, or other yardwaste that is raked into a stormdrain

Exemptions- it is ok for the following to enter the storm sewer system: 

  • Landscape irrigation
  • Discharges from potable water sources
  • Air conditioning condensate 
  • Water from crawl space pumps
  • Foundation drains

Illicit Discharge Warning Signs

The most obvious way to spot an illicit discharge is during dry weather. Since storm sewer systems exist to carry stormwater runoff, they are generally active during rain events or during times of heavy snowmelt. In a neighborhood or at a commercial site, look for pipes in disrepair or hoses that lead to a stormdrain or body of water. Look for stains, suds, unusual odors, structural damage to streets or gutters, and abnormal vegetative growth in nearby lakes and streams. 

  • Dry Weather Flow is noted when it has not rained for at least 72 hours and the storm drain has flow or the drain shows signs of intermittent flow (staining, odor).
  • Sanitary Sewage may be present if there is black staining inside the drainage pipe; visible evidence of sanitary waste, such as toilet paper; or opaque or gray water.  Sewage may originate from septic tank overflow pipes or improperly dumped travel trailer waste. 
  • Suds may be harmful to fish because suds deplete oxygen levels in the water.  Suds often enter lakes and streams as a result of improperly connected car washes or washing machines. 
  • Oil/Gas is recognized as a sheen on the water. Natural sheens may be differentiated from an oil/gas sheen by swirling the sheen around in the water. If it re-attaches, the sheen is oil/gas. Natural sheens will remain separated. Oil/Gas enters waterbodies via storm water runoff (spills while topping off at gas stations, oil leaks on pavement, etc.) and illegal dumping.


To protect the quality of our streams and public health, please report sources of pollution you witness along the roadside, roadside parks, or in your neighborhood, including:

  • Dumping waste/oil or other vehicle fluids
  • Suspicious pipes outletting to ditches
You can do this anonymously by contacting your local community officials here or by calling the pollution emergency alerting system (PEAS) hotline at: 800-292-4706 if your community is not listed.

Besides reporting Illicit Discharges, there are many other things that you can do to protect water quality! Check out just a few of our pollution solutions here

Please Report Illegal Discharges!

The information on this page was originally from Michigan Department of Transportation (MDOT) and can be found here.

Only Rain in the Drain