"This report summarizes the results of an unprecedented nationwide assessment of human effects on fish habitat in the rivers and estuaries of the United States. The assessment assigns watersheds and estuaries a risk of current habitat degradation ranging from very low to very high. These results allow comparison of aquatic habitats across the nation and within 14 sub-regions. The results also identify some of the major sources of habitat degradation. Unfortunately, not all sources of habitat degradation could be assessed, so some important factors such as small dams and abandoned mines could not be incorporated. Marine waters, lakes, and reservoirs were not assessed due to resource and data constraints, so previously published information was used to describe the condition of these fish habitats. Future revisions to the assessment will incorporate the missing data to the extent it is available"--Executive summary.