The objective of this project is to create a new macroinvertebrate bioassessment index that can be applied at both the regional and reach scales to make status determinations. A bioassessment index developed for use at multiple spatial scales would benefit multiple agencies, Federal, State, and local, as well as public and private organizations by giving them a tool that can help them identify sites/watersheds in need of protection, preservation and/or restoration. Use of aquatic macroinvertebrates as bioindicators of stream condition can be incorporated into a decision-support model (DSM) which can be used as a method towards assessing overall watershed condition. The capacity of the DSM to make accurate condition and trend determinations is dependent upon the sensitivity of the individual attributes used to define watershed condition. Therefore, in the case of macroinvertebrates, it is critical to identify the optimal bioassessment index, as well as the factors influencing index performance.