Storm Water Runoff
Storm water runoff is anything that is carried by rainwater down into our drainage systems. This includes the water that falls on roofs, lawns or on paved areas like driveways, sidewalks, parking lots and streets across our city. As this water flows over these surfaces, it picks up debris, chemicals, sediments, and other pollutants and carries them into our storm sewers.
During a storm, patches of rain may only fall in certain places, but runoff flows across the ground everywhere. The City manages thousands of miles of public streets, sidewalks and drainage channels.
Understanding how rainfall runoff carries everyday pollutants is an important first step in knowing how to reduce and prevent them from contaminating water. Clean, healthy waterways support safe water for drinking, swimming, fishing and recreation and provide habitat for wildlife.
Runoff: How It Pollutes
Common Pollutants
Most runoff pollutants come from chemicals in everyday products and bacteria from waste that we and others dump on the ground. These include:
- household hazardous waste (HHW) products (indoor pesticides, cleaners, paint, polishers, thinners, cooking oil)
- automotive fluids (motor oil, transmission fluid, antifreeze, car washing soaps/cleaners)
- lawn and garden insecticides/herbicides
- pet or other animal fecal wastes
Why It Matters
Unlike wastewater flushed from sinks and toilets, storm water runoff is not treated or filtered. Instead, it flows into channels that empty directly into rivers and creeks. Over time, these pollutants can make the water unsafe and unhealthy for fish, vegetation, wildlife and people.
Impacts on Rivers & Creeks
Pollutants such as chemicals from HHW products, automotive fluids and lawn care products can poison and destroy fish and aquatic plants that live in rivers and creeks. Animals and people can get sick from eating diseased fish or drinking polluted water.
These pollutants also reduce oxygen levels in water, which can cause algae blooms, suffocate aquatic life and damage habitats.
San Antonio River Basin
The San Antonio River Basin is a widespread system of rivers, creeks and stream channels that drain an area of more than 4,000 square miles. Major basin watersheds include the Medina River, Leon Creek, Upper/Lower San Antonio, Salado Creek and Cibolo Creek watersheds.
The San Antonio River flows 240 miles from San Antonio/Bexar County into the Guadalupe River in Refugio County, where it eventually drains into the San Antonio Bay and Gulf of Mexico.
Learn more about the basin by visiting the San Antonio River Authority webpage.
San Antonio River & Wildlife
The river and neighboring riparian areas are home to a variety of local animals, fish, plants and other wildlife species, including:
- Native Fish
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Largemouth Bass, Flathead Catfish, Longear Sunfish, Channel Catfish, Red Shiner
- Native Reptiles/Amphibians
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Comal Blind Salamander, Bullfrog, Rio Grande Leopard Frog, Diamondback Water Snake, Blotched Water Snake, Common Snapping Turtle, Red-Eared Slider, Texas River Cooter
- Native Mammals
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Common Raccoon, White-Tail Deer, Nine-Banded Armadillo, Easter Cottontail Rabbit, Collared Peccary, Opossum
- Native Birds
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Double-Crested Cormorant, Whooping Crane, Mallard, Osprey, Snowy Egret, Belted Kingfisher
- Native Plant Species
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American Water-Willow, American White Waterlily, Floating Primerose-Willow, Herb of grace, Manyflower Marshpennywort, Yellow Pond-Lily
The San Antonio River Authority education team's mission is to inspire citizens of all ages to take action in their communities toward the stewardship and sustainability of the San Antonio River and its tributaries.
The education team aims to accomplish this mission by utilizing the best environmental education practices and tools necessary for students of all ages to create and carry forward their own innovative environmental best management practices.
Discover more facts and history about the San Antonio River's source, length, development and diverse native wildlife species by visiting the San Antonio River Authority Education webpage.
Impacts of Polluted Runoff
When polluted storm water runoff enters our rivers and creeks through our drainage system, chemical pollutants, hazardous bacteria and other wastes can affect the oxygen levels and nutrient balances needed by native fish, plants, animals and humans for survival:
- Fish and plants inhabiting the rivers and creeks can suffocate, mutate and die off as pollutants infiltrate the water.
- Animals who rely on the water as a natural drinking source can suffer poisoning, disease and decreased numbers.
- River and creek water can become impaired over time, gradually making the rivers and creeks unsafe for swimming, fishing and other recreational activities.
Polluted runoff also poses risks to our very own drinking water. Water from our rivers and creeks flows into natural recharge zones which feed into our Edwards Aquifer. Left unchecked, runoff pollutants can infiltrate these recharge zones and threaten the water we rely on daily. While systems and controls are in place to help mitigate this risk, runoff water quality continues to be an important issue and priority in the overall health of our drinking water.
For information on drinking water quality, see the San Antonio Water System (SAWS) Water Quality Report.