ABSTRACT
Reference conditions are a set of physical, chemical, and biological conditions that describe the characteristics of the most minimally impaired streams in a given ecoregion or subecoregion. Although derived from a set of measurements acquired from typical reference stream sites in a relatively homogeneous region, the reference condition is based upon a composite of those characteristics and is not, therefore, site specific. An established reference condition provides a basis for making comparisons and making determinations on impairment or degree of impairment for a newly sampled stream in that same ecoregional unit (Gibson et al. 1996).
