Stream Bioregions

In 1992, the U.S. Environmental Protection Agency (EPA) defined ecoregions and subregion as areas "within which there is an apparent homogeneity in a combination of geographic characteristics that are likely to be associated with resource quality, quantity and type of stresses." Regionalization was performed as a collaboration among DEP, water management districts and the U.S. EPA Environmental Research Laboratory in Corvallis, Oregon.

The main issue for the evaluation of bioassessment data was to establish regional reference conditions for ecosystem health through a selection of subregional sites. To determine a subregional reference condition, sites were selected on least-disturbed streams with small catchments and completely within subregion.

Using this process, over 100 subregional reference sites were originally selected by U.S. EPA. subregion are aggregated into bioregions based on similarities in their macroinvertebrate communities. 

Bioregions are then used as the geographical basis for the assignation of community health thresholds. 

• View Bioregions on map.