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Undeveloped or grassy (pervious) areas, such as parks and lawns, soak up most of the rain that falls there. Therefore, there is much more polluted stormwater runoff in areas with large amounts of impervious, or non-porous surfaces. Stormwater from urban areas is one type of 'nonpoint source' pollution - pollution that comes from many diffuse sources. The stormwater picks up all the pollutants along its pathway. It is often referred to as “Polluted Runoff.” Because polluted stormwater runoff is caused by so many of our everyday activities, we all need to work together to prevent it!

Stormwater picks up and carries numerous pollutants into our waterways. Many of these pollutants can cause problems in very small amounts. The cumulative effects of stormwater runoff on water bodies are evident in both of our Rivers and in Rock Creek. The Potomac and Anacostia Rivers, that regularly receive untreated stormwater, now suffer from poor water quality. Pollutants in stormwater may include antifreeze, grease, oil, and heavy metals from cars; fertilizers, pesticides and other chemicals from gardens, homes and businesses; bacteria from pet wastes and failing septic systems; and sediment from poor construction site practices. If not properly managed, the volume of stormwater can flood and damage homes and businesses, flood septic system drainfields, erode stream channels, and damage or destroy fish and wildlife habitat. Because less water soaks into the ground, drinking water supplies are not replenished and streams and wetlands are not recharged. This can lead to water shortages for people and inadequate stream flows for fish.

Uncontrolled stormwater runoff has many cumulative impacts on humans and the environment including:

• Flooding - Damage to public and private property
• Eroded Streambanks - Sediment clogs waterways, fills lakes, reservoirs, kills fish and aquatic animals
• Widened Stream Channels - Loss of valuable property
• Aesthetics - Dirty water, trash and debris, foul odors
• Fish and Aquatic Life - Impaired and destroyed
• Impaired Recreational Uses - Swimming, fishing, boating
• Threatens Public Health - Contamination of drinking water, fish/shellfish
• Threatens Public Safety - Drownings occur in flood waters
• Economic Impacts – Impairments to fisheries, shellfish, tourism, recreation related businesses
• Increased Cost of Water and Wastewater Treatment - Stormwater pollution increases raw water treatment costs and reduces the assimilative capacity of waterbodies.

Excess stormwater causes flooding and damage that is difficult and costly to clean up.