What is stormwater and why does it matter?

Stormwater is rain or melted snow that falls on lawns, streets, roofs, and other surfaces . It is different from sanitary sewage that drains from your sinks, showers, and toilets.

When it rains, water probably leaves your yard through eave spouts or by running off the lawn and driveway. The flowing water picks up fertilizers, pesticides, animal waste, and other contaminants and flows off of your grass, onto the sidewalk, and into the street. The polluted water may flow into a storm drain by the street's curb and disappear from sight.

You might think that stormwater, like sanitary sewage, is cleaned after it is out of sight. Those chemicals from your neighbor’s lawn are probably filtered out before the stormwater reaches the Illinois River, or all of that stormwater must be carried in pipes through tanks and filters to remove contaminants. After all, we want to boat, swim, and fish in clean creeks and streams that smell nice and look clear, right?

Here's the thing: stormwater that leaves your yard, gutters in your neighborhood, farm fields, and city streets is not treated before it gets to the river. It might enter a storm drain that directly empties into a creek. It might enter a storm drain that empties into a ravine, where the water washes down the ravine faster and faster and collects soil from the ravine's sides until it eventually joins a larger creek that reaches the river. It might flow over land or through drainage channels into another water body. Whatever happens, all of that storm water drains into our rivers.

This water can carry chemicals, animal waste, litter, and other pollutants into the river. It also carries sediment, or dirt, which causes other problems. But if the bottom of the river consists of dirt, why is it harmful to have sediment in the river?

There are several ways that sedimentation harms the river and the animals and people nearby:

• Valuable topsoil from farmland can end up in New Orleans instead of on our fields. Topsoil and pollutants flow from our land into the creeks that feed the Illinois River; water from the Illinois River flows to the Mississippi River and the Gulf of Mexico.
• Sediment creates polluted, murky water that suffocates fish and prevents sunlight from reaching aquatic plants. These plants are a necessary start to the food chain in the river, so if they can’t grow, fish, birds, and other animals have a harder time finding food.
• Extra sediment that enters the river partially fills the navigable channels of the river. Barges, sailboats, and other boats have less room to navigate.

Sedimentation is an expensive problem to fix, but it is more expensive to allow sedimentation to continue. For example, a local marina has become so filled with sediment that it must be dredged, and dredging will have to continue as long as sedimentation occurs. However, we can all do our part to minimize this problem. Click on a watershed to see what you can do to keep our water clean.