The amount of nutrient and sediment pollution that flowed from nine major rivers into the Chesapeake Bay remained below the 25-year average in 2013. While scientists expect this to have a positive impact on the long-term health of the nation’s largest estuary, much of the Bay’s tidal waters remain impaired: between 2011 and 2013, just 29 percent of the water quality standards necessary to support underwater plants and animals were achieved.

Excess nutrients and sediment are among the leading causes of the Bay’s poor health. Nitrogen and phosphorus can fuel the growth of harmful algae blooms that lead to low-oxygen “dead zones” that suffocate marine life. Sediment can block sunlight from reaching underwater grasses and suffocate shellfish. Lowering the amount of nutrients and sediment moving from our streets, lawns and farm fields into the water is a critical step in the restoration of the Bay, and scientists have attributed the below-average pollution loads of 2013 to below-average river flow and the pollution-reducing practices our partners have put in place on the land.

Because pollution in our rivers has a direct impact on water quality in the Bay, the Chesapeake Bay Program tracks both environmental indicators to gain a wider picture of watershed health.

Our partners at the U.S. Geological Survey (USGS) monitor nutrient and suspended sediment loads delivered from the large watersheds located upstream of nine river monitoring stations to the Chesapeake Bay. Together, these stations—which are located on the Appomattox, Choptank, James, Mattaponi, Pamunkey, Patuxent, Potomac, Rappahannock and Susquehanna rivers—reflect loads delivered to the Bay from 78 percent of its watershed. Data show that nutrient and sediment loads measured in water year 2013 were below the long-term average.

  • About 160 million pounds of nitrogen reached the Bay during the 2013 water year, which is below the long-term average of 212 million pounds. Between 1985 and 2013, trends in total nitrogen concentrations improved at five out of nine sites, including the James, Patuxent, Potomac, Rappahannock and Susquehanna rivers. Over the past decade, trends in total nitrogen concentrations have improved at three sites and declined at one site.
  • About 10 million pounds of phosphorus reached the Bay during the 2013 water year, which is below the long-term average of 14.6 million pounds. Between 1985 and 2013, trends in total phosphorus concentrations improved at three sites, including the James, Patuxent and Potomac rivers. Over the past decade, trends in total phosphorus concentrations have declined at two sites. Other sites experienced no significant change.
  • About 2.71 million tons of sediment reached the Bay during the 2013 water year, which is below the long-term average of 5.2 million tons. Between 1985 and 2013, trends in suspended sediment concentrations have improved at three sites, including the Choptank, Patuxent and Potomac rivers. Over the past decade, trends in total sediment concentrations have declined at four sites. Other sites experienced no significant change.

The Chesapeake Bay Program measures progress toward the achievement of water quality standards in the Bay and its tidal tributaries using three environmental factors: dissolved oxygen, water clarity or underwater grass abundance, and chlorophyll a. Data are assessed in three-year periods. After more than a decade of steady improvement between 1989 and 2002, the attainment of water quality standards has seen mixed results. Changes seen in the past 10 years have not been statistically significant, and it is likely that the slow recovery of underwater grasses in the Upper Bay has stalled some water quality improvements.