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chapter | 
Introduction 
In April 2003, the U.S. Environmental Protection Agency (EPA) published the Am¬ 
bient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a 
for the Chesapeake Bay and Its Tidal Tributaries (Regional Criteria Guidance) in 
cooperation with and on behalf of the six watershed states—New York, Pennsyl¬ 
vania, Maryland, Delaware, Virginia, and West Virginia—and the District of 
Columbia. The culmination of three years of work, the criteria document resulted 
directly from the collective contributions of hundreds of regional scientists, technical 
staff, and agency managers as well as the independent review by recognized scien¬ 
tific experts across the country (U.S. EPA 2003). 
In October 2004, EPA published the first addendum to the 2003 Regional Criteria 
Guidance (U.S. EPA 2004). The addendum provided additional guidance on: 
• Applying the temperature-based open-water dissolved oxygen criteria required 
to protect the endangered shortnose sturgeon; 
• Assessing attainment of the instantaneous minimum and 7-day mean dissolved 
oxygen criteria using monthly mean water quality monitoring data; 
• Deriving site-specific dissolved oxygen criteria and assessing criteria attain¬ 
ment of those tidal systems where the extensive adjacent tidal wetlands cause 
naturally low dissolved oxygen levels; 
• Delineating the upper and lower boundaries of the pycnocline that defines the 
vertical boundaries distinguishing open-water, deep-water, and deep-channel 
designated uses; 
• Applying, in combination, the numerical water clarity criteria to shallow water 
habitats and submerged aquatic vegetation restoration goal acreages for 
defining attainment of the shallow-water bay grass designated use; and 
• Determining where numerical chlorophyll a criteria should apply to local 
Chesapeake Bay and tidal tributary waters. 
From 2004 through early 2006, Delaware, Maryland, Virginia, and the District of 
Columbia adopted: the EPA-published Chesapeake Bay water quality criteria for 
chapter i 
Introduction 
