how does stormwater runoff affect the environment

How Does Stormwater Runoff Affect the Environment?

Last Updated on August 12, 2023 by Annie Baldwin

Stormwater runoff refers to rainwater or melted snow that runs off streets, lawns, and other sites and flows into storm drains and water bodies.

Stormwater runoff can have a variety of detrimental effects on the environment, highlighting the importance of understanding and addressing its impacts.

This article explores the consequences of stormwater runoff and why it matters.

How Does Stormwater Runoff Affect the Environment?

How does stormwater runoff affect the environment?
Rain that falls on the ground has two possible outcomes: either it soaks into the soil and becomes groundwater, or it runs off the surface and becomes runoff. The soil serves as a “filter,” capturing and holding onto nearly everything that the rainwater carried with it as it percolates into the earth.

Stormwater runoff degrades water quality and harms aquatic ecosystems through the various pollutants it collects as it travels across urban landscapes.

Contaminated runoff threatens biodiversity, clean drinking water, and public health.

Key Points

  • Stormwater becomes polluted as it travels across impervious surfaces, picking up contaminants like sediment, nutrients, bacteria, chemicals, and trash.
  • Polluted runoff degrades habitat, threatens aquatic life, and creates unsafe conditions in recreational waters and drinking water supplies.
  • Green infrastructure practices like rain gardens and permeable pavement allow for onsite treatment and absorption of stormwater.

What are the Main Causes of Stormwater Runoff?

The two main causes of stormwater runoff are the large amounts of impervious surfaces in urban environments and the poor management of stormwater.

Impervious surfaces like roads, parking lots, driveways, and rooftops prevent rain and snowmelt from naturally soaking into the ground.

Instead, these surfaces cause water to rapidly run off into storm drains, carrying various pollutants.

Urban areas contain high percentages of impervious surfaces, significantly increasing runoff.

Additionally, inadequate stormwater management leads to excessive runoff volumes entering waterbodies untreated.

Common practices like channeling runoff directly into storm drains rather than implementing green infrastructure allow runoff to bypass natural filtration.

Proper stormwater management using green infrastructure could dramatically reduce runoff volumes and treat stormwater onsite before it becomes problematic.

How Does Stormwater Runoff Negatively Impact Water Quality?

Stormwater becomes contaminated as it travels across urban landscapes, picking up numerous pollutants that degrade water quality:

  • Sediment – Erosion washes sediment from construction sites and other disturbed soils into a runoff, degrading habitat, and water clarity.
  • Nutrients – Fertilizers, animal waste, and organic matter contribute nutrients like nitrogen and phosphorus that promote algal blooms and eutrophication.
  • Bacteria – Fecal matter from pets, wildlife, and leaking sewage introduces pathogenic bacteria like E. coli and viruses.
  • Toxic chemicals – Vehicles, pesticides, cleaning products, and industrial processes release heavy metals, hydrocarbons, and other toxic substances into runoff.
  • Trash and debris – Cigarette butts, plastic bags, styrofoam, and other garbage wash into and accumulate in water bodies.

Without proper management, these various contaminants enter waterways, degrading water quality and threatening aquatic life, wildlife, and human health.

How Does Contaminated Stormwater Runoff Affect Aquatic Ecosystems?

The pollutants in stormwater runoff have numerous detrimental effects on freshwater and marine ecosystems:

  • Sediment clouds waters, blocking sunlight and harming aquatic plants. It also clogs fish gills and smothers bottom-dwelling organisms.
  • Excess nutrients fuel algal blooms, which deplete oxygen in the water when they die off and decompose. Low oxygen levels suffocate fish and bottom-dwellers.
  • Bacteria and other pathogens in runoff waste make water unsafe for human contact and recreation. Pathogens can also sicken aquatic life.
  • Toxic chemicals accumulate in sediments and aquatic organisms, causing developmental and reproductive damage. They may bioaccumulate up the food chain.
  • Debris entangles and is ingested by aquatic wildlife like fish, turtles, birds, and mammals, often leading to injury, starvation, and death.

Overall, polluted stormwater degrades habitat, threatens biodiversity, and creates unsafe conditions for aquatic life.

It can gravely impact entire ecosystems.

What Are Some Solutions for Managing Stormwater Runoff?

How does stormwater runoff affect the environment?
As they say, “When it rains, it pours,” but the tough part is what happens next. The runoff from too much rain becomes a muddy, toxic mess when it combines with fertilizers, pesticides, animal feces, and other harmful substances from your yard. There are many ways of controlling stormwater flow in your yard. Image Credit: Lawn Love

While the problems caused by stormwater runoff are complex, various management solutions can help:

  • Installing green infrastructure like rain gardens, green roofs, and porous pavement to capture, absorb, and filter runoff onsite.
  • Implementing and enforcing stricter regulations on stormwater management for development projects.
  • Retrofitting existing infrastructure in urban areas with green infrastructure practices to intercept runoff.
  • Educating homeowners, businesses, and developers on stormwater management best practices for their properties.
  • Using low-impact development (LID) approaches that preserve natural areas capable of absorbing runoff.
  • Regular street sweeping, installing trash filters, and implementing pet waste stations to reduce pollution flowing into storm drains.
  • Creating and restoring wetlands and riparian buffers capable of filtering runoff before it enters waterbodies.

Addressing stormwater at its source is crucial for preventing it from becoming polluted runoff.

Green infrastructure and LID techniques offer the most promise for sustainable stormwater management.

Why Should We Be Concerned About Stormwater Runoff?

Stormwater deserves serious attention because of its severe, widespread impacts on waterbodies, wildlife, and human populations.

Polluted runoff threatens biodiversity, aquatic ecosystems, clean drinking water, and public health.

This complex problem has no single solution.

However, a lack of concern and inaction will inevitably lead to continued environmental degradation and health hazards.

Implementing green stormwater infrastructure wherever possible is an important step toward creating more sustainable, ecologically friendly urban areas.

Managing stormwater runoff is essential to protect the health of both people and ecosystems.

Why Is Runoff Important To The Environment?

Stormwater runoff is crucial to the environment because it provides fresh water to ecosystems.

However, in developed areas, it becomes contaminated with pollutants and degrades water quality in streams, rivers, lakes, and coastal waters.

Stormwater in urbanized areas can contain high concentrations of heavy metals, sediments, nutrients, bacteria, and toxic chemicals.

When this polluted runoff enters water bodies, it has severe impacts on aquatic habitats and organisms.

Runoff is a vital contributor to the health of aquatic ecosystems.

Rain and snowmelt provide clean water that replenishes rivers, wetlands, lakes, and groundwater.

This influences salinity levels, oxygen content, and nutrient balances that allow ecosystems to thrive.

But when runoff becomes contaminated, it disrupts the chemical, biological, and physical integrity of aquatic habitats.

The pollutants in stormwater can alter water conditions to levels that are unsuitable for many species to survive and reproduce.

Managing and treating stormwater is crucial to ensure runoff does not harm the environment.

What Is One Environmental Problem Storm Water Runoff Poses?

One of the most significant environmental problems caused by polluted stormwater runoff is the contamination of drinking water sources.

Runoff often carries hazardous chemicals, heavy metals, pesticides, fertilizers, bacteria, and solid waste from roads, construction sites, lawns, farms, and industrial facilities into rivers, lakes, and reservoirs that supply drinking water.

This compromises water quality and safety, increasing risks to public health.

Studies have found stormwater runoff to be responsible for high concentrations of pollutants in drinking water reservoirs.

These contaminants are difficult and expensive to treat or remove.

Pathogens, trace metals, nutrients, and toxic organic chemicals pose the greatest problems for drinking water treatment systems.

Stormwater pollution also contributes to algal blooms in reservoirs, contaminating treated drinking water with algal toxins.

Poorly managed stormwater runoff poses major challenges and health threats for communities that rely on surface water for drinking.

Preventing polluted runoff from entering source waters is crucial to providing clean, safe drinking water.

How Does Stormwater Pollution Affect Humans?

When stormwater enters water bodies untreated, carrying contaminants and toxins, it creates significant risks to human health.

Bacteria from animal waste can infect recreational waters, causing illness in swimmers.

Nutrient pollution fuels harmful algal blooms that release toxins capable of causing neurological impairments.

Chemical toxins bioaccumulate in fish and shellfish, contaminating seafood.

Trash and debris accumulate along coastlines, creating safety hazards.

Studies have directly linked stormwater runoff to increases in waterborne illness in humans.

The Centers for Disease Control estimates that up to 3.5 million people get sick from contact with sewage-polluted coastal waters each year.

Children are especially vulnerable, and respiratory illnesses from red tide algal blooms have also been documented.

Consuming contaminated seafood can cause intestinal, neurological, and skin illnesses, liver and kidney damage, and developmental issues in children.

Stormwater pollution also threatens drinking water quality.

Chemical toxins have been documented in public water supplies at levels exceeding health advisory limits.

Polluted runoff degrades source waters, increasing cancer risks and the potential for long-term health effects.

Overall, contaminated stormwater creates significant health hazards, especially for children, the elderly, and immunocompromised populations.

How Does Channeling Runoff Directly Into Storm Drains Affect The Environment?

Traditional stormwater management directs runoff from roads and other impervious surfaces directly into storm drains through gutters, pipes, and artificially straightened stream channels.

This conveys stormwater rapidly into waterways without any filtration or treatment of contaminants.

Channeling runoff with grey infrastructure short-circuits the natural processes that would otherwise filter and purify water.

Plants, soil, wetlands, floodplains, and riparian areas absorb and filter runoff, removing sediments, nutrients, and other pollutants.

Minimizing these types of landscapes while maximizing impervious surfaces and grey infrastructure severely degrades water quality.

Directly piping contaminated urban and suburban runoff into rivers, lakes, estuaries, and oceans threatens aquatic ecosystems.

Rapid influxes of polluted stormwater disrupt habitat, feed algal blooms, affect salinity levels, introduce toxins, and expose wildlife to pathogens and debris.

This channelized conveyance system overwhelms waterbodies with contaminated runoff anytime it rains, negatively impacting water quality and ecosystem health.

In Summary

Stormwater runoff is one of the greatest threats to clean and safe water due to its ability to collect and carry numerous pollutants.

It has detrimental effects on water quality, aquatic ecosystems, and human health.

While the problem is challenging, green infrastructure and low-impact development offer workable solutions for intercepting and treating runoff before it damages the environment.

With proper stormwater management, many of its worst impacts could be mitigated.


What types of pollutants does stormwater runoff carry?

Stormwater picks up and transports various contaminants as it flows across urban environments, including sediment, nutrients, bacteria, heavy metals, toxic chemicals, trash, and debris. These pollutants come from lawns, roads, industrial sites, vehicles, and many other sources.

How do the pollutants in stormwater runoff impact the environment?

The contaminants carried in stormwater have numerous damaging effects, such as reduced water clarity, algal blooms, oxygen depletion, illness in aquatic species, bioaccumulation of toxins, and the injury or death of wildlife from ingesting debris. Overall, polluted runoff degrades habitat, harms biodiversity, and threatens entire ecosystems.

What practices can be implemented to reduce stormwater runoff pollution?

Green infrastructure, low-impact development, public education programs, pet waste management, street sweeping, waterway cleanups, wetland restoration, and redevelopment policies that include stormwater treatment requirements can all help mitigate contaminated runoff.

How can homeowners help address stormwater pollution?

Homeowners can install green infrastructure like rain barrels, rain gardens, and permeable pavers to capture and filter runoff from roofs, driveways, and patios. They should also limit fertilizer use, properly dispose of hazardous wastes, pick up pet waste, and prevent soil erosion on their properties.

GreenChiCafe is passionate about the environment and protecting ecosystems and wildlife from pollution. Check out more of our sustainability content on our website!

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