As water runs across the land during precipitation events, it can pick up pollution that is on the land surface (litter, manure, chemicals, fertilizers, etc.).  Runoff containing pollution flows untreated directly into our streams or down storm drains. Runoff that enters storm drains then flows untreated into local streams we use for swimming, fishing, boating, etc.

As we increase the amount of hard surfaces that don’t allow water to soak into the ground, such as driveways, sidewalks and streets, more water runs off. Because less water is soaking into the ground, underground water supplies are not replenished.

This increased runoff also leads to more frequent flood events, as there is less area for rainfall or snowmelt to soak into the ground. Not
only do these flood events occur more frequently, they are often more catastrophic.

Increased runoff also leads to increased erosion of stream banks because the velocity of water flowing through streams is greater. This causes more dirt to enter our streams, clogging habitat for aquatic life and making it difficult for aquatic life to survive.
 

Did you know...the hard surfaces of a city block can generate five times more runoff than a wooded area of the same size!