In order to facilitate more effective integration of monitoring data and technically sound assessment methodologies into the waterbody assessment and listing process, a critical evaluation of the current methodologies employed by the states was recognized by WERF. Funding was provided to document and evaluate current assessment and listing methodologies employed by the states during the development of their Integrated Reports.The findings from the review of current waterbody assessment methodologies presented herein provides a comprehensive overview of the current state of the science for the waterbody assessment and listing process. Using the strengths found in many of the states assessment methodologies and information found in other guidance, the Research Team developed recommendations which request the states to:1) develop and publish minimum data quantity and quality requirements,2) better integrate monitoring programs with waterbody assessment needs,3) develop standardized assessment units that allow for better water quality extrapolation,4) develop numeric water quality criteria by which to more reliably determine support or impairment of designated uses,5) use statistically-based data evaluation techniques to more confidently determine attainment of water quality standards, and6) include the public in the assessment and listing methodology development process.