The United States is home to a diverse array of freshwater and marine fish, shellfish, and other aquatic species. More than 3,000 species of fish inhabit America’s streams, rivers, lakes, reservoirs, marshes, swamps, bays, estuaries, coral reefs, seagrass beds, shallow water banks, deep ocean canyons, and other aquatic habitats. The United States is also home to more than 322 million people
, 39% of whom live near the coasts
and all depending on the same water that fish call home. In 2012, approximately 25 percent of the nation’s acreage was agricultural and 6 percent was developed
. However, these and other consequences of human inhabitation affect much broader areas by altering water flow (hydrology), water quality, and many aquatic habitat characteristics. Few aquatic habitats in America have been or are currently unaffected by human activity and some have been severely degraded. Map 1 depicts the results of the habitat assessments conducted for this report, with the estuarine areas offset for better visibility. Assessments of lake, reservoir, offshore marine, and Great Lakes habitats were not conducted because of resource limitations but are, at least in part, expected to be completed for the 2020 National Fish Habitat Assessment if resources are allotted.
Overall, 22 percent of inland stream mileages in the lower 48 states are at high or very high risk of current habitat degradation, and 62 percent are at low or very low risk. Areas of high and low risk of current habitat degradation occur in discernable patterns. Stream habitats with a very high risk of current habitat degradation include: those watersheds in or near urban areas, areas with a high number of pastures and hay fields, areas with high amounts of row crop agriculture, systems with many point sources of pollution, and those with high numbers of active mines or dams in their watershed. Generally, agricultural land use had a broader, negative effect on assessment results than any other variable. However, the accumulation of all development variables typically resulted in the most severe disturbances.
Specific regions of pronounced high risk of current habitat degradation include: the urban centers of Boston to Washington DC, Atlanta, Dallas, Houston, Chicago, Denver, Southern California, San Francisco area, Honolulu, and Seattle to Eugene; and the agricultural regions of the Midwest from Ohio to North Dakota, northwestern New York, the Mississippi River Basin, northwestern Texas, northwestern Utah, southern Idaho, northern Montana, central California, and southeastern Washington. Streams and rivers in the Central Midwest have the greatest risk of degradation in the nation. Even though these are broad areas that are evident on the national scale, many aquatic habitats throughout the country are threatened. Key problematic locations will be noted in the Regional sections of this report.
Areas that stand out as being at very low risk according to the parameters evaluated in this assessment include: rural areas in New England and the Great Lakes states; many habitats throughout the Rocky and Appalachian Mountains; the Southwest; and most of Alaska. Overall, the states of the Southwest have the lowest risk of habitat degradation of the 14 regions assessed using the available landscape data but this is likely an overestimate of the quality of the habitat as a result of our inability to fully include water flow (hydrology) or intensive grazing as variables.
It is critical to note that not all water and land management issues could be addressed in the assessment as consistently measured data are not available for all issues. Many variables are not available nationally, so some of the areas mapped as being at low risk of current habitat degradation actually may be at higher risk due to disturbance factors not assessed.
For example, most arid regions of the western United States were found to be at low risk of current habitat degradation. Water quantity is a critical limiting factor for 179 species of desert fishes
, yet water flow (hydrology) was not accounted for in the assessment as hydrology data is unavailable for many river and stream reaches. Additionally, intensive grazing using poor management practices in riparian zones (upland areas next to streams and rivers) has caused significant aquatic habitat degradation in these same areas. The assessment likely overestimates the amount of habitat at low risk of current habitat degradation in the arid West as hydrologic alterations, such as water withdrawals, and grazing are key driving factors that could not be fully assessed in this report. However, if issues of hydrologic alterations and intensive grazing could be improved, the arid West has the potential to be at low risk of degradation.
The estuaries of the lower 48 states show patterns similar to those of the land areas as shown in Map 1, which is not surprising because most of the disturbances to estuarine habitats originate on land. Estuaries in the mid-Atlantic and in Peninsular Florida have a high or very high risk of habitat degradation related to pollution issues and other effects of the intense urban and agriculture land uses. The estuaries of Southern California, the San Francisco area, and the Seattle area also have a very high risk of current habitat degradation for similar reasons. Generally, pollution and land cover were the most limiting stressors of the eastern coastal habitats, and reduced river flow typically had greater effects on estuaries of Texas and the Pacific coast. Nutrient loading, or eutrophication
, was also a significant factor leading to higher degradation risk in the estuaries of the mid-Atlantic and Texas.
Many of the estuaries in the northern Pacific States Region, the Florida Panhandle, Georgia, South Carolina, and Maine had a low or very low risk of current habitat degradation. This assessment could not examine Alaskan estuaries as the result of limited funding, but based on the inland assessment of low risk, it is likely that Alaska’s estuarine habitats also have low risk of degradation except in a few localized areas near population centers. Overall, 32 percent (by area) of the estuaries in the lower 48 states are at low or very low risk of current habitat degradation, while 46 percent are at high or very high risk of current habitat degradation.
We would like to emphasize that comparisons should not be made between the 2015 and 2010 reports because additional variables were assessed in 2015 and the statistical methodology was greatly improved for determining risk categories. Work is underway to develop additional comparable change metrics to allow comparisons of like data and will be available in the future.