The primary function of the VTDEC Biomonitoring and Aquatic Studies Section (BASS) is to conduct environmental monitoring of Vermont's surface waters, with an emphasis on the assessment of biological integrity. Activities include: the collection, processing and analysis of biological samples; the collection of physical habitat and water chemistry data; the assessment of monitoring data results to determine biological health and water quality; and the integration of those assessments into a wide variety of DEC management programs. BASS conducts over 200 comprehensive biological assessments annually, with emphasis on evaluation of fish and aquatic macroinvertebrate communities in wadeable streams and rivers. BASS has also conducted special studies in areas of special concern, and has assisted in data collection and/or analysis for other programs like the USEPA and the VTDEC Lakes and Ponds Management and Protection Program. Vermont DEC routinely surveys the macroinvertebrate and fish communities of rivers, streams, lakes and wetlands in order to evaluate the biological health, or biological integrity, of the ecosystem surveyed. This type of survey is called biomonitoring. Biomonitoring surveys are used for detecting aquatic life impairments and assessing their relative severity. These surveys can also be used to identify very high quality surface waters in need of enhanced levels of protection. The Ambient Biomonitoring Network (ABN) program was established by the Vermont DEC in 1985 to monitor long-term trends in water quality as revealed in changes over time to ambient aquatic fish and macroinvertebrate communities, to evaluate site-specific impacts of point and non-point discharges to aquatic biological communities, and to establish baseline data to assist the Department in establishing Vermont-specific biological criteria for water quality classification attainment determinations in rivers and streams. Since 1985, the Department has used standardized methodologies for sampling fish and macroinvertebrate communities, evaluating physical habitat, processing samples, and analyzing and evaluating data. The program has led to the development of a Vermont-specific fish community Index of Biotic Integrity (IBI) and guidelines for determining water quality classification using macroinvertebrate community biological integrity metrics. The aquatic macroinvertebrate data contained here primarily represent the data that has been collected by BASS or private consultants and used to assess the biological integrity of wadeable streams, based on the functional and compositional characteristics of the sampled community. These samples are assessed using the biological metrics described in Appendix G of the Vermont Water Quality Standards (https://dec.vermont.gov/watershed/tasc/water-quality-standards). There is also a breadth of data included that represent special studies and other biomonitoring initiatives. These include data from the USEPA's National Rivers and Streams Assessment, pilot biomonitoring surveys for Vermont's lakes and ponds, artificial substrate colonization studies, and statewide species distribution surveys for mussels, crayfish, and other macroinvertebrates.