In April 2003, the U.S. Environmental Protection Agency (EPA) published the Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries which was the foundation document defining Chesapeake Bay water quality criteria and recommended implementation procedures for monitoring and assessment (U.S. EPA 2003a). This document represents the fifth formal addendum to the original 2003 Chesapeake Bay water quality criteria document. As such readers should regard the sections in this document as new or replacement chapters and appendices to the original published Bay Criteria report (U.S. 2003a). The criteria assessment procedures published in this addendum also replace and otherwise supersede similar criteria assessment procedures published in the 2004, 2007 and 2008 addenda (U.S. EPA 2003a, 2004a, 2007a, 2007b, 2008). Publication of future addenda by EPA on behalf of the Chesapeake Bay Program watershed jurisdictional partners is likely as continued scientific research and management applications reveal new insights and knowledge that should be incorporated into revisions of state water quality standards regulations in upcoming triennial reviews.