The first release of CADDIS in 2006 provided a step-by-step process for rigorously identifying the stressors causing undesirable biological changes in aquatic systems and   organizing the scientific evidence supporting the conclusions, based on EPA’s 2000 Stressor Identification Guidance document.  It included downloadable worksheets and examples, and began a library of conceptual models.  New material, added in 2007, provides introductory information and conceptual models for commonly evaluated candidate causes including metals, sediments, nutrients, ionic strength, dissolved oxygen, temperature, and flow.  In addition, we have added analytical tools to help users explore stressor-response associations using their own data.  This material is available in external review form now, and is expected to be finalized by September 2007.