Stormwater Pollution SourcesUnderstanding What Pollutes Our Waterways
Our Water, Our Responsibility
Many people think of pollution as something that comes from a factory pipe or a major spill. While those sources can impact water quality, much of the pollution affecting local waterways comes from everyday activities in our neighborhoods, businesses, parks, and communities.
When rain falls or snow melts, water flows across rooftops, streets, driveways, parking lots, and lawns. As it moves, it can pick up pollutants and carry them into storm drains, ditches, streams, rivers, and lakes.
Understanding where stormwater pollution comes from is the first step toward preventing it.
What Is Stormwater Pollution?
Stormwater pollution occurs when rainfall or snowmelt picks up pollutants and transports them into local waterways.
Unlike wastewater, stormwater is generally not treated before it enters streams, rivers, lakes, or wetlands. Because of this, anything left on the ground has the potential to become a water quality concern.
Common stormwater pollutants include:
- Sediment (soil and dirt)
- Pet waste
- Fertilizers
- Pesticides
- Grass clippings
- Leaves
- Trash and litter
- Vehicle fluids
- Household chemicals
- Road salt and deicers
Many of these pollutants originate from ordinary activities that occur every day.
Point Source vs. Non-Point Source Pollution
Water pollution is often grouped into two categories: point source pollution and nonpoint source pollution.
Point Source Pollution
Point source pollution comes from a single, identifiable location.
Examples may include:
- Industrial discharge pipes
- Wastewater treatment plant outfalls
- Certain permitted discharges
Because the source can be identified, these discharges are often easier to monitor and regulate.
Non-Point Source Pollution
Nonpoint source pollution comes from many small sources spread across a landscape.
Examples include:
- Fertilizer washed from lawns
- Pet waste left on the ground
- Oil dripped from vehicles
- Leaves and grass clippings in streets
- Trash carried by runoff
Nonpoint source pollution is one of the most common water quality challenges because it results from many individual actions rather than a single source.
Sediment and Soil Erosion
Most people don’t think of dirt as pollution.
However, when rain washes soil from one place to another, that soil can end up in streams, rivers, lakes, and wetlands. Sediment is one of the most common pollutants affecting waterways across the United States.
Bare soil is especially vulnerable during heavy rain. Construction sites, eroding streambanks, and other disturbed areas can all contribute sediment to stormwater runoff.
Keeping soil where it belongs helps keep waterways cleaner.
Pet Waste
Pet waste is more than an unpleasant sight—it can also affect water quality.
Pet waste contains bacteria, nutrients, and other pollutants that can be washed into waterways during rain events. When waste is left on sidewalks, trails, parks, or yards, stormwater runoff can carry those pollutants into local streams and lakes.
Picking up after pets is one of the easiest ways to help protect water quality.
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Fertilizers and Pesticides
Lawns and gardens can be beautiful additions to a community, but improper use of fertilizers and pesticides can impact water quality.
Excess nutrients such as nitrogen and phosphorus can be washed into waterways during rainfall. These nutrients may contribute to algae growth and reduced water quality.
Following label directions, applying products only when needed, and avoiding application before rainfall can help reduce runoff.
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Leaves and Grass Clippings
Leaves and grass clippings may be natural materials, but they can still contribute to water pollution.
As yard waste breaks down, it releases nutrients that can enter waterways and contribute to water quality problems. Yard waste can also clog storm drains and reduce drainage capacity.
Keeping leaves and grass clippings out of streets, gutters, and storm drains helps protect local waterways.
Trash and Litter
Trash left outdoors can easily become stormwater pollution.
Plastic bottles, food wrappers, cigarette butts, fireworks debris, and other litter can be carried by runoff into waterways. Once there, these materials may persist for years and can harm wildlife and aquatic habitats.
Proper disposal of trash and participation in cleanup efforts help reduce litter pollution.
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Vehicle Fluids
Vehicles can leak oil, antifreeze, transmission fluid, brake fluid, and other chemicals onto streets and driveways.
Even small leaks can accumulate over time. During rainfall, these pollutants may be carried into storm drains and nearby waterways.
Routine vehicle maintenance helps prevent leaks and protects water quality.
Household Chemicals
Many common household products can become pollutants if disposed of improperly.
Examples include:
- Paints
- Solvents
- Cleaning products
- Automotive chemicals
- Pool chemicals
These materials should never be dumped into storm drains, ditches, gutters, or waterways.
Always follow local disposal guidelines and use household hazardous waste collection programs when available.
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Winter Pollution
Stormwater pollution is not limited to warm weather.
During winter, snowmelt can carry road salt, deicers, sand, and other materials into stormwater systems and waterways.
These products help improve safety during icy conditions, but applying more than necessary can increase environmental impacts.
Using products carefully and according to label directions helps balance safety and water quality protection.
Wildlife Feeding and Water Quality
Feeding ducks, geese, and other wildlife may seem harmless, but it can contribute to water quality problems.
Concentrating wildlife in one location often increases the amount of waste entering nearby waterways. Additional nutrients from wildlife waste can affect water quality and contribute to algae growth.
Supporting healthy habitats rather than feeding wildlife helps maintain more balanced ecosystems.
How Pollution Reaches Waterways
Stormwater runoff acts as a transportation system for pollutants.
When rain falls on developed areas, runoff flows across the landscape and enters storm drains, ditches, channels, and waterways. Along the way, it can pick up pollutants left on the ground.
Because stormwater is not treated before entering local waterways, preventing pollution at the source is one of the most effective ways to protect water quality.
What Residents Can Do
Everyone can play a role in protecting local waterways.
Simple actions include:
✓ Pick up pet waste
✓ Keep leaves and grass clippings out of streets
✓ Use fertilizers carefully
✓ Properly dispose of household chemicals
✓ Maintain vehicles to prevent leaks
✓ Secure trash and recycling containers
✓ Follow product label directions
✓ Avoid dumping anything into storm drains
Frequently Asked Questions
Why is dirt considered pollution?
While soil belongs on the land, it can become a pollutant when it is washed into waterways. Excess sediment can reduce water quality, harm aquatic habitat, and carry nutrients and other pollutants into streams, rivers, and lakes.
Is pet waste really considered pollution?
Yes. Pet waste contains bacteria and nutrients that can affect water quality when carried into waterways by runoff.
Why are leaves and grass clippings considered pollutants?
As they break down, they release nutrients that can contribute to water quality problems and algae growth.
Can stormwater carry oil and gasoline?
Yes. Vehicle fluids deposited on streets and driveways can be transported by runoff during rainfall.
Are fertilizers harmful to waterways?
When applied improperly or in excess, fertilizers can contribute nutrients that affect water quality.
Does road salt impact water quality?
Road salt and deicing products can enter waterways through snowmelt and runoff, which is why careful application is important.
What is the most important thing I can do to reduce stormwater pollution?
Prevent pollutants from being left where rainfall can wash them into storm drains and waterways.