As water flows off of our streets, parking lots, and building rooftops, it picks up all kinds of pollutants like pet waste, sediment, fertilizers, pesticides, oil, and automotive fluids. If it does not evaporate or soak into the ground—nature's "green filter"—and if untreated or poorly treated, the contaminated runoff adversely affects water quality and aquatic life in local streams, the rivers into which they feed, and ultimately the Chesapeake Bay. As more houses, roads, and shopping centers are built, more of this polluted stormwater or runoff makes its way through gutters and storm drains to the nearest stream.
Urban and suburban polluted runoff is the only major source of nitrogen pollution in the Bay still growing. Though responsible for greater percentages of pollution, agriculture and sewage treatment plants have made progress. Better stormwater management is an increasingly necessary—but admittedly expensive—proposition for local governments.
As impervious surfaces channel large quantities of rainwater into streams at high velocity, the runoff wreaks havoc. The flow scours stream banks, destabilizes stream contours and alters depths. It muddies drinking water sources and also carries bacteria, making the treatment and use of such water more expensive.
In the Bay's tributaries, eroded material and dirt from the land become suspended in the water, blanketing aquatic habitat. This sediment keeps sunlight from reaching underwater grasses. As these plants die, the animals that rely on them are imperiled.
And it is not only wildlife that is endangered by stormwater pollution. The state of Maryland, for example, cautions people not to swim in waterways for 48 hours after a heavy rain. Stormwater carrying bacteria has resulted in serious illnesses. In urban and suburban areas where ground surfaces have been hardened and the polluted water has no place to go, local streets and basements often flood, causing repeated and costly damage to homes and businesses.
According to the Environmental Protection Agency (EPA), urban and suburban stormwater is the source of about 15 percent of the total nitrogen entering the Bay, and is the only source that is still increasing. In some rivers it makes up an even higher percentage of the problem. It is one of the major reasons that the Bay remains on EPA's "dirty waters" list and is now subject to the Chesapeake Clean Water Blueprint.
Additional information about stormwater management can be found at the following websites: