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Water Quality Standards Achievement for Chlorophyll a

Results of the 2013 to 2015 assessment period indicate that 3 percent of the tidal water segments of the Chesapeake Bay that contain the open-water habitat designated use met water quality standards for chlorophyll a (a measure of algae growth).

  • Data (59.7 KB)       

July 22, 2011

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Excess nutrients and sediment are among the leading causes of the Chesapeake Bay’s poor health. Both can impact the clarity of water and the amount of algae and oxygen it contains. This indicator measures the achievement of water quality standards for chlorophyll a in the Bay.

Water quality standards for the Bay were developed in 2003 by the U.S. Environmental Protection Agency (EPA). Within these standards, five aquatic habitats—also called “designated uses”—were identified, each with its own criteria for dissolved oxygen, water clarity/underwater grasses and chlorophyll a. If the Bay and its tidal tributaries are to function as a healthy ecosystem, all designated uses must meet all clean water criteria.


In 2014, the Chesapeake Bay Program adopted a goal to reduce pollution and achieve the water quality necessary to protect human health and support the region’s underwater resources.

Additional Information

Analyzing data

The methodology used to calculate this indicator considers the achievement or non-achievement of water quality standards for chlorophyll a in the 7 tidal water segments that contain the open-water habitat designated use.

This indicator uses a surface area-weighted approach, which takes the relative size of each segment into account and ensures we report the best available measure of water quality standards achievement in the Bay.

Reporting data

The University of Maryland Center for Environmental Science reports a chlorophyll a indicator that tracks data in all tidal waters, not in relation to Bay water quality standards. The indicator is updated annually and is available online.

Source of Data

Chesapeake Bay Program

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