Threats to Water Quality

There are two types of pollution that affect the quality of our watersheds:

1. Point source pollution

This is pollution that comes from a specific point, such as a factory or an industrial plant. While most environmental regulations deal with point source pollution, the majority of watershed pollution comes from non-point source pollution.

Photo by Mary Jo Adams.

2. Non-point source pollution

Non-point source pollution comes from many different sources and cannot be traced to a single point. Non-point source pollution includes pollutants that are picked up by stormwater and drain into watersheds. Non-point source pollution includes:

Agricultural runoff
Pesticides, herbicides, fungicides, and other chemicals that farmers use for their crops or animals combine with the water that drains into the watersheds. These chemicals, in addition to animal waste, can lead to harmful bacteria polluting the water supplies.

Urban runoff
Urban runoff is also known as storm drain pollution. Rainwater drains from buildings, sidewalks, parking lots, lawns, and other urban areas and collects all the contaminants that were on the surfaces such as synthetic fertilizers, pesticides, grease, chemicals, animal droppings, etc. These pollutants drain into the storm drains and into a larger body of water.


Image from the Mill Creek Watershed, Ohio website.

Urban development is a threat to watersheds as it changes the path that water flows. When a watershed begins to be developed, plants are replaced with impervious cover, such as roads, parking lots, sidewalks, driveways, and buildings which hinder stormwater’s ability to soak into the ground. Stormwater that cannot be absorbed into the ground becomes stormwater runoff, which can lead to erosion of streams and creeks. In addition to erosion, stormwater runoff tends to be very contaminated as it picks up debris as it flows.

Urbanization also leads to habitat degradation, vegetation removal, and invasive species.

Septic sewage
According to the US EPA, an estimated 10 to 20 percent of onsite private waste water treatment systems malfunction each year, polluting the environment and causing public health risks.  Contaminants from septic systems include bacteria and viruses nutrient pollutants such as nitrates, and household chemicals that may have been disposed of down the drain or toilet.  Proper septic system maintenance can prevent such pollution.

For information on maintaining your septic system contact the McLean County Health Department or consult the EPA’s Septic Smart Program.