The colloquium contains two major sections--an overview and a more lengthy set of background papers by individual authors. The participants at the colloquium concluded that a national water quality monitoring and assessment program, in some form and at some level of effort, is warranted in order to improve comprehensiveness and reliability of information for decisionmaking. Among the reasons cited for having such a national program included the need to improve: characterization of the general quality of the nation's water resources; understanding of water quality trends, specifically changes showing improvement or worsening in conditions; understanding of the extent, nature, and causes of water pollution so as to suggest ways of protecting human health and the environment; setting of standards and assurance of compliance with regulations; development of water quality control technology; quality assurance/quality control efforts so as to ensure greater consistency, compatibility, and reliability of data collection; data base management and information exchange; understanding of aquatic phenomena; and predictive capability.