The objective of this classification was to create a simplified set of stream and river habitat types based on the Northeast Aquatic Habitat Classification System (Olivero and Anderson 2008) and GIS map for 13 northeastern states (ME, NH, VT, MA, RI, CT, NY, PA, NJ, DE, MD, VA, WV, and DC.) that could be used in the Northeast Stream and River Habitat Guide (available at http://nature.ly/HabGuide). The goal was to collapse the existing 258 types down to ~25 types for reporting in the habitat guide. The habitat guide contains a description of each stream and river type, a distribution map, a photo, associated common and rare species, a crosswalk to state aquatic community types, and a summary of current condition information. Given the scope of the project, the existing Northeast Aquatic Habitat Classification System (Olivero and Anderson 2008) and GIS map (NHD Plus V1. 1:100,000) was used as the foundation. Resources were not available for remapping at a finer scale or reanalyzing the detailed stream and river types in the region, although a new tidal stream and river class was developed as part of this simplification project. The simplification method was developed with guidance from a steering committee of state freshwater ecologists. The steering committee recommended using a simplification framework based on the NY Freshwater Blueprint (White et al. 2011).

To keep the number of regional types to a manageable number yet still maintain key ecological information, we developed a 58 type simplification that used size, gradient, geology, temperature, and tidal classes. However, the above five variables were not used to define every habitat type. For example, headwaters through small rivers were split using size, gradient, geology and temperature, while medium to large rivers were only split by gradient and temperature. Tidal habitats were split by three size classes. This simplification yielded a set of stream and river types that many felt would be useful to agencies and managers across the region. For the general audience of the habitat guide, the 58 types were further collapsed into 23 major types. The 23 major types were created by collapsing the geology classes for headwaters through small rivers and collapsing the gradient classes for medium to large rivers. Although the expected natural community types within the various geology classes of headwaters through small rivers will vary, particularly among the macroinvertebrate and aquatic plant communities, we wanted to focus the general audience on the more dominant patterns of size, gradient, and temperature for headwaters through small rivers. Similarly for medium to large rivers, we focused on the dominant patterns of size and temperature variation within these larger rivers. The habitat guide maps still show the finer distribution of the full 58 types using different colors for geology types within headwaters-small rivers and different colors for gradient classes for medium-large rivers, however the accompanying habitat guide descriptions, associated species, and condition statistics reflect patterns across the simplified 23 types.