You may not have heard of runoff, but you've definitely seen it.

It's those curbside streams rushing into thirsty drains during a big rainstorm; the steady trickle down a soapy driveway as you wash your car. 

Runoff is surface water that can't absorb into the ground before it reaches a waterway. In developed areas, more pavement means fewer opportunities for the water to soak in.

Runoff picks up all the oils, chemicals, dirt and pollution it finds on the road and other paved surfaces and washes them down the storm drain. Those contaminants flow into the nearest catch basin, which ultimately drains into nearby lakes and rivers. 

This can pollute the water and upset the local ecosystem. The excess water can even contribute to flooding.