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Biological assessments, particularly benthic macroinvertebrate surveys, are used to designate waters as impaired for not supporting the waters aquatic life use. However, biological assessments do not identify the cause(s) of the impairment. A reliable stressor identification process is required to accurately identify the cause(s) of the water quality degradation that affects the benthic community. This paper describes the U.S. Environmental Protection Agencys (EPA) stressor identification process and demonstrates its use for TMDL development on six streams with benthic impairments. An interdisciplinary advisory panel of experts followed the EPA process and used their collective best professional judgment to identify the causes of impairment in the studied streams. The group first listed a set of candidate causes based on information obtained from benthic macroinvertebrate survey reports, published literature, visual surveys, and stakeholder input. Chemical and physical monitoring of the study streams provided additional evidence to support or eliminate the potential candidate causes. By using this information and the stressor identification process, the critical stressor(s) were identified, and six TMDLs were completed and approved by EPA.