What is

Stormwater is the product generated when rainwater comes in contact with an impervious surface, pollutants, and impurities.

For example, precipitation lands on a parking lot, road, or roof top, collecting accumulated trash and chemicals as it flows over the surface.

This process leads to stormwater pollution. A major global water quality and environmental concern.

Why is
Stormwater a Problem?

Stormwater pollution and its affects reach far beyond the immediate source and local community.

Stormwater can cause flooding, erosion, and pollution leading to large environmental, health, and economic issues.

And if polluted runoff is not addressed, these hazardous flows can cause complications far downstream and away from the original source.

How does
Stormwater collect contaminants?

As stormwater pools and flows across impervious surfaces, it gathers plastics, trash, debris, oils, and other pollutants along the way. Some of these materials are even naturally occurring or organic materials, such as leaves, branches, grass, and soil. However, harmful chemicals and pesticides can bind to these materials, like plastics and sediment. Furthermore, organic material can breakdown and contribute to harmful nutrient and bacteria levels for the environment.

The Pollutants in
Stormwater Runoff?

Stormwater can contain various pollutants like micro plastics, large trash, pet waste, chemicals, oils, grease, tire or rubber crumb, and other yard waste or pesticides.

Urbanization and
Stormwater Runoff

Expanding urban areas or locations undergoing new development involve a considerable amount of land movement, and high-traffic impervious surfaces. As a result, these areas can have a significant impact on stormwater pollution.

Because concrete is not porous, it forces the flow of stormwater. As a result, urban or metropolitan areas are key locations where stormwater becomes polluted. On top of the rapid spread of stormwater in these areas, commercial and personal pollutants are more common—including trash, chemicals, and assorted debris.

What is
Urban Stormwater Runoff?

Impervious surfaces include roads, parking lots, sidewalks, and even roofs. As storms or melting snow generates excessive water, the water flows freely across these types of urban surfaces and into storm drains, bringing any pollutants with it.

As stormwater flows downstream, water volume and the concentration of pollutants can also increase.

Therefore, polluted stormwater can amass surprisingly fast, leading to high concentrations of pollutants and debris flowing downstream. If untreated or managed properly, stormwater can overwhelm watersheds, drainage system, and sensitive water bodies; causing long-term damage or environmental issues.

Where Does
the Stormwater Pollution Come From?

Stormwater pollution can be generated in many ways, but it is most common in developing and high-traffic areas.

Stormwater tends to collect in storm drains associated with an urban areas associated industrial sites, streets, parking lots, and common areas.

Why is
Stormwater Pollution a Problem?

Stormwater may not be one of the most well-known forms of pollution compared to greenhouse gas emissions, or oil production pollution, but it is a major issue worldwide.

Polluted water affects rural areas, urban watersheds, large ecosystems, and rural and recreational waters where oils, pet waste, and trash are collected and swept into waterways.

Sea life, fish, aquatic ecosystems, and human health are all at threat from stormwater pollution. In addition, our communities are susceptible to floods, damage, and long-term effects.

Isn’t Stormwater Treated
Before Going into the Ocean?

Stormwater Pollution Prevention Plan

Unfortunately, stormwater is not always treated as comprehensively as waste water. Sewer systems and networks work to direct blackwater to treatment plants, but storm drains usually manage flows differently. Managing volume from different sources, but not always addressing the contaminants involved.

Due to its nature and volume, stormwater is not typically combined with wastewater treatment systems. In most cases, stormwater is diverted via a passive system and directed to nearby waterways.

What Legislation Governs
Stormwater Pollution?

Stormwater pollution is governed by several different laws that attempt to address pollutant hazards.

This includes the Environment Protection Act of 1993, the Environment Protection (Water Quality) Policy of 2003, and the Development Act of 1993, among a few others.

A 1996 EPA report to U.S. Congress noted, “Urban runoff is the leading source of pollutants causing water quality impairment related to human activities in ocean shoreline waters.”

Stormwater Pollutants & Where they come from

Chemical Pollution

Any number of chemical goods or waste can be very harmful to the natural world, particularly fertilizers, oil, grease, detergents, fuel, or vehicle and tire byproducts.

Chemical pollutants have a longer period of contamination in the environment, because they cannot naturally of safely bread down and decompose.


Trash and debris are easily created by humans but not always disposed of properly, which makes them incredibly prevalent in stormwater. Litter such as cigarette butts, food wrappers, plastic bags, cans, and even paper are all widespread stormwater pollutants and cause massive environmental issues and various aquatic habitats.

Natural Pollution

Even naturally occurring substances can pollute water bodies, especially when released in large quantities.

Organic materials such as leaves and garden clippings can contribute to stormwater pollution.

In large quantities, other naturally occurring pollutants, like sediment and pet waste can harm water bodies.

Gross Pollutants

In general, gross pollutants refer to anything larger than sediments, either organic or manufactured.

Such gross pollutants are common in industrial or urban areas, including trash, debris, or natural substances like leaves.

Heavy Metals

Poisonous in large amounts, heavy metals are spread into stormwater and subsequent waterways easily because they cannot be broken down like some natural pollutants and will stay present in water for a long time. Structural wear and tear, vehicle damage, and even atmospheric deposition are responsible for heavy metal pollutants in stormwater.

Structural wear and tear, vehicle damage, and even atmospheric deposition are responsible for heavy metal pollutants in stormwater.

Water Temperature

One of the lesser-known issues associated with stormwater pollution is increased water temperature. This is caused by runoff from solid surfaces or plants removed from the edges of water bodies. And because these conditions foster easy growth of harmful plants and algae, aquatic life is significantly and negatively impacted.


Animal waste runoff, faulty septic tanks, or overflowing/overwhelmed sewer systems can contribute a variety of risky micro-organisms to stormwater as well.

Animal waste
Overflowing sewers

These bacteria and viruses can lead to a variety of fatal illnesses in animals and humans, including cryptosporidium and gastroenteritis.

Contributing Material

Excessive amounts of nutrients reduce oxygen levels and have harmful effects on aquatic species and plant life. Algae growth can also obstruct water flow and contribute to drainage failures.

Oils & Soaps

Oils, detergents, and shampoos in stormwater can come from industrial spills, car washing, or automotive leaks, and pose threats to water ways and ecosystems.

Absorbing Substances

Various substances create biochemical oxygen demand when placed in water, including byproducts from animal feedlots, pulp mills, or food processing facilities.

Unfortunately, these substances break down to oxygen-requiring bacteria that remove oxygen from the water around it, harming, aquatic wildlife, plants, and other organisms dying.

pH Levels

Stormwater pollution can change the pH values of the nearby waterways.

Incredibly high or low pH levels in water can be harmful to habitats, animals, and humans.

These pH levels can make water corrosive or acidic, leading to environmental and safety issues.


While some sediment transfer is expected in stormwater runoff, large amounts displaced by construction or vehicles are very harmful to the environment.

Toxic Organics

Toxic organics can be found in lawn and garden care products, pesticide, herbicides, and industrial waste.

Because these byproducts are highly toxic, they poison aquatic life and plants when introduced to local bodies of water.

Effects of Stormwater Pollution

Now that we are familiar with the causes and types of stormwater pollution, we can discuss the problems that arise from it. And these effects are not constrained to the environment and wildlife—stormwater pollution negatively impacts people and cities just as severely. The following issues are just a few of the variety of problems that stormwater pollution causes.

Economic Impacts

There are various industries, like fishing, farming, tourism, and even real estate, that rely on clean and safe water, so stormwater pollution can have adverse economic affects.

Water is life and the foundation of many economic pillars.

And because contaminated stormwater spreads so quickly and without management, pollutants will not affect just one business, as the polluted stormwater continues to travel downstream.

In addition, tourism and recreational activities are harmed by polluted stormwater. Waterways that have floating trash and debris or smell terrible due to waste or bacteria are not conducive to visitors. As such, the tourism and recreation sectors will suffer great economic losses because of this.

Eroded Stream Banks

Another stormwater pollution threat lies on the banks of waterways. Stormwater can erode stream banks quickly, carrying the sediment and material along with it. This sediment goes on to clog other waterways and even destroy ecosystems that aquatic life depends upon.

High volumes of mismanaged stormwater can suddenly and damage river banks, streams, and lakes, erosion and widening river banks can threaten land and communities.


Not only does stormwater carry pollutants, but it also deposits them in unsafe locations. In addition, pollutants like sediment or debris can cause blockages, leading to water backup and flooding.

Heavy rain events are one of the most common contributors to mass flooding, and proper storm drain systems are just a part of managing sudden increases in volume to prevent flooding. Stormwater system, detention and retention systems can also help manage volumes and often prevent inundation and flooding of roads and property.

Foul Odors and Aesthetics

Between dirty water, trash, and debris, polluted stormwater can be responsible for various foul odors.

As bacteria form during the natural decomposition of a variety of pollutants, foul odors are released into the air and can spread across a surprisingly large distance. In addition, pollutants cause a rise in algae growth, creating a layer of surface scum that has a terrible smell.

Stormwater can cause a range of environmental issues, but it also looks bad.

Stormwater collects but can also spread and distribute trash and debris, impacting recreation and tourism.

Impact on Fish & Aquatic Life

Plastic bags, bottles, six-pack rings, and cigarette butts are all dangerous to fish and waterfowl.

Additionally, sediment and nutrients spread by stormwater can smother the delicate ecosystems present in wetlands, river mouths, and inlets. These pollutants reduce the amount of sunlight exposure that reaches plants and animals and encourages harmful plants and algae to grow.

Impairment of Recreational Uses

Chemicals, bacteria, and waste present in stormwater pollution are all hazardous to human health, so when these pollutants enter water bodies, they become unsafe to enjoy.

For example, swimming in polluted waters can lead to a variety of sicknesses and health issues, including ear infections and digestive issues.

Threats to Public Health

Because of the bacteria and harmful micro-organisms in stormwater pollution, it poses a significant risk to public health. Polluted stormwater affects sources of drinking water, and swimming in contaminated stormwater can lead to a variety of illnesses, including cryptosporidium, gastroenteritis, and a variety of parasites, all harmful to humans.

Due to public health risks, beach and waterway closures are most common in polluted stormwater drainage areas, negatively impacting people’s quality of life and economic development. Seafood that comes from highly contaminated areas can also pose significant health risks to consumers.

Widened Stream Channels

Instability in stream channels is another issue that is caused by stormwater pollution. The larger the urban area, the more polluted stormwater nearby waterways are forced to accommodate. And the force with which stormwater can enter waterways not only causes erosion issues initially but over time, works to widen the entire stream channel.

This widening leads directly to stream channel instability that affects the waterway and the surrounding land. Turbid conditions, exposed stream banks, fallen trees, and more are all part of widened stream channels, as well as heightened safety risks. And in urban areas, the widening of stream channels can cause extensive damage to public and private property.