Students

Stormwater Pollutants 101
When it rains, it pollutes!

Rain and melting snow act like a water hose, washing the landscape free of loose dirt and grime. While a good washing helps spruce up our communities after a long winter or summer dry spell, it does little for the health of our rivers, lakes and wetlands. That is because materials washed off the hard surfaces in our towns and cities eventually end up in the water, where they can become harmful pollutants.

Pollution caused by rain and snowmelt washing the landscape goes by several names. It is called stormwater pollution because it is caused by storms, runoff pollution because it is carried by rain and snowmelt runoff, and nonpoint-source water pollution, a technical name meaning it is different than point-source water pollution. Point source water pollution is the type of water pollution that comes from an industrial or wastewater discharge pipe — a definite point, or location, on the landscape.

Controlling stormwater pollution is a challenge because sources of pollution come from many locations across the landscape and is associated with weather — something we cannot control. Controlling stormwater pollution requires everyone’s action, from the homeowner to the business owner, from the road builder to the street sweeper.

The main stormwater pollutants harming Minnesota’s waters are:
Sediment
Nutrients
Bacteria
Toxics
Heat

Sediment
Sediment is dirt from our roads, and eroded soil. A major source of sediment in urban areas is construction sites where exposed soil is easily washed or blown away. Once it finds its way to water, sediment fills in rivers, lakes and wetlands, destroying wildlife habitat, interfering with recreation, and causing flooding. Sediment also carries other stormwater pollutants with it, such as nutrients and toxics which adhere to soil particles.

Nutrients
Nutrients are plant food, which by itself is a good thing — fertilizers help our gardens, lawns and farm fields grow — but too much plant food entering water can cause an overabundance of algae growth. Algae are small free-floating water plants that turn water green, slimy, and smelly when they grow in abundance. The nutrient of most concern in phosphorus — one extra pound of phosphorus added to a lake can produce up to 500 pounds of algae! Phosphorus is the biggest pollution problem for Minnesota lakes, so the Minnesota legislature passed the Phosphorus Lawn Fertilizer Law, which restricts the use of phosphorus-containing lawn fertilizer. A less known but significant source of phosphorus is your car. The brakes and tires of cars as well as gasoline are made up of a phosphorus so it is important to maintain your vehicle and use care when filling the gas tank of your car.
Bacteria
High levels of fecal bacteria, bacteria found in feces, have caused swimming beach closings in the Twin Cities metro area. The bacteria come from pet and wildlife feces that wash into the lakes with stormwater. Pick up after your pet and do not feed wildlife.

Toxics
Toxics refer to such poisons as pesticides, salt, and metals such as lead, copper and zinc. Sources of toxic materials vary greatly and include yard chemicals, road salt, seepage from storage yards, and metals coming off roofing materials and car brake pads. Although more alarming-sounding than sediment and nutrients, effects of toxic materials on lakes and rivers are harder to identify. Studies in the Twin Cities, however, show that the numbers of different types of plants and animals in wetlands with high levels of chloride (salt), zinc and copper are lower than what are found in natural wetlands.

Heat
It might be hard to think of heat as a pollutant unless you’re a cold-water fish such as trout. Trout require water temperatures of 60 to 65 degrees. Stormwater running off hot roofs, roads and parking lots in the summer can easily raise stream temperatures above what is safe for trout. In addition, warm water temperatures can accelerate the growth of algae. With all our hard surfaces that heat up in the summer, keeping cool is a big challenge for CRWD’s lakes and the Mississippi River.


Students Grades 3-5

Whatever is in the street ends up in our lakes and rivers. See what’s wrong with this watershed picture.