Stormwater runoff occurs when rain runs over lawns, sidewalks, streets, roofs, driveways, and other impervious surfaces that do not allow water to soak into the ground. As the water flows over surfaces it cannot seep through, it can pick up harmful pollutants such as sediment, nitrogen, phosphorus, bacteria, oil and grease, trash, chemicals, and metals. These pollutants come from a variety of sources such as pet waste, litter, lawn fertilization, cars, construction sites, illegal dumping and spills, and pesticide application. When water has no way to enter the ground, it will keep travelling above ground until it hits the nearest lake, canal, river, and eventually the ocean.
Why is it a problem?
Since this water had no opportunity to deposit whatever it grabbed along the way, it deposits that matter into the water body, where it can begin to have negative effects on the waterways and its surrounding ecosystem. Stormwater is not treated, and therefore has the potential to harm people, animals, and plants:
Excessive amounts of nutrients from fertilizers and herbicides that are carried to lakes may lead to algae to grow faster than ecosystems can handle (called algal blooms), blocking light needed for aquatic plant growth (known as eutrophication). When these algae and plants die, their decay reduces or eliminates oxygen in the water, leading to illnesses and death of marine life. Some algal blooms produce elevated toxins and bacterial growth that can make humans sick if they come in contact with polluted water, consume tainted fish or shellfish, or drink contaminated water.
Chemicals such as pesticides, herbicides, fertilizer, motor oil, gasoline, cleaners, paints, and other automobile chemicals can be washed into waterways and be harmful to the health of humans and wildlife, and destroy aquatic plants.
Sediments washed from construction areas, human land use, and soil erosion causes waters to become cloudy, preventing natural vegetation from growing in water and animals from seeing food sources. Sediment also fills up storm drains and catch basins to carry water away from roads and homes, increasing the potential for flooding.
Bacteria and viruses from human and animal fecal matter can be washed into water sources, leading to possible contamination of drinking water and illness in people who recreationally use surface waters such as beach areas with high bacteria counts. It is important to pick up and properly dispose of pet waste.
Solid garbage such as plastic bottles, cigarette butts, plastic bags, and plastic straws can kill animals such as turtles, birds, and fish by suffocating or choking them. Many animals mistake a small piece of plastic for food and ingest this waste, which blocks their digestive tracks and causes them to starve. Furthermore, toxic chemicals in plastic can harm animal’s health, and people can ingest these chemicals as they make their way up the food chain in a processes known as bioaccumulation and biomagnification.