These data represent Endangered Species Act critical habitat designated for Atlantic salmon (Gulf of Maine DPS). The final rule for this designation can be found in the Federal Register at 74 FR 29300 (June 19, 2009).

Critical habitat for Atlantic salmon (Gulf of Maine DPS) includes the stream channels within the designated stream reaches, and includes a lateral extent as defined by the ordinary high-water line (33 CFR 329.11). In areas where the ordinary high-water line has not been defined, the lateral extent will be defined by the bankfull elevation. Bankfull elevation is the level at which water begins to leave the channel and move into the floodplain and is reached at a discharge which generally has a recurrence interval of 1 to 2 years on an annual flood series. Critical habitat in estuaries is defined by the perimeter of the water body as displayed on standard 1:24,000 scale topographic maps or the elevation of extreme high water, whichever is greater.Watershed boundaries provide a standard level of detail that is an acceptable unit to describe salmon habitat, and the watershed level 5 (HUC 10s) are nationally recognized by the USGS to spatially relate any dataset that contains these codes.