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• Pollutant loads continue to exceed target levels established to restore the Bay's water quality. Additional pollution-fighting measures are being put in place throughout the watershed to reduce pollution loads in the future.
• Annual Chesapeake Bay water quality conditions are largely determined by a combination of the amount of pollution deposited on the land or discharged in wastewater and the amount of water flowing into the Bay. As the volume of water flowing into the Bay – or river flow – increases, its potential to carry increased pollutants increases as well. Scientists estimate annual pollutant loads to the Bay through a combination of monitored water samples and modeled information. Whenever practical, scientists measure pollution levels in water samples from the rivers and wastewater pipes that flow into the Bay. Model-generated estimates are used where monitoring is not practical, when no data are available or data do not meet specific requirements and/or are outdated.
• By capturing water samples at the point where large, free-flowing rivers meet tidal waters, scientists can calculate pollution loads from 78 percent of the watershed land area. For the remaining area, loads from wastewater and model-generated estimates are used. This combination of monitoring and modeling data allows scientists to provide the most practical accounting of the amount of pollution reaching the Bay.
• The Bay's watershed covers an enormous 64,000-square-mile area that includes parts of six states – Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia – and all of the District of Columbia. Billions of gallons of water flow each day through thousands of streams and rivers that eventually empty into the Bay. The Bay must process runoff from a large amount of land with a relatively small body of water.
• Runoff from winter and spring rains deliver loads of sediment and nutrient pollutants to the Bay that drive summer water quality conditions in the Bay. Past observations reveal that summer weather conditions also contribute to summer water quality when intense storms increase erosion, which contributes to poor water clarity and adds to the existing nutrient load in the Bay.
• Not all rain water “runs off” the land. Some water seeps into the soil, carrying nutrients into groundwater. The travel time of nutrients through the watershed ranges from weeks to centuries. This can result in a “lag time” between implementing management actions and improvements in water quality.

• Sources of Nitrogen Loads to the Bay
• Nitrogen Loads Delivered to the Bay from Municipal and Industrial Wastewater
• Nontidal Nitrogen Loads and River Flow To the Chesapeake Bay

For more information contact: Katie Foreman at 800-968-7229 ext. 837

Chesapeake Bay Program