Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

Review the indicators at a glance

Chemical and Physical Conditions

Three indicators describe the chemical and physical condition of fresh waters; these are complemented by several related measures included in other chapters (see below). Two indicators focus on water quality: the concentration of phosphorus, a vital plant nutrient that can lead to problems if present in excess, and the clarity of lake and reservoir waters. Water quantity is also important, so a third measure tracks changes in key flow characteristics of streams and rivers.

Because it is important to all ecosystems, many additional indicators of water quality are presented elsewhere in this report. These include core national indicators dealing with nitrogen and contaminants such as pesticides, PCBs, and heavy metals in streams, sediment, groundwater, and fish. There are also measures dealing with nitrogen or phosphorus or both in the farmlands (nitrogen, phosphorus), forest (nitrogen), grasslands and shrublands (nitrogen), and urban and suburban (nitrogen, phosphorus) chapters and indicators dealing with contaminants in the farmlands and urban and suburban chapters.

• How much phosphorus is there in lakes, reservoirs, and large rivers? About half of all river sites tested had phosphorus concentrations that exceeded the Environmental Protection Agency’s recommended level for preventing excess algae growth. Data are not adequate for national reporting on phosphorus in lakes. See phosphorus in farmland streams and phosphorus in urban and suburban streams for data on phosphorus in smaller streams.
• How many streams have had major changes in the size or timing of their lowest or highest flows since the 1930s–1940s? Changes in these key flow characteristics can disrupt the plants and animals that live in or near streams. The percentage of streams with major changes in the size of their highest or lowest flow, or in the timing of these flows, increased slightly (from 55% to 60%) from the 1970s to the 1990s. The number of streams with high flows that were well above the 1930–1949 reference period increased markedly from the 1980s to 1990s.
• How clear are lakes in the United States? Lakes in some regions are normally quite clear; in other places, lakes are less clear because of naturally occurring algae, sediment, and other suspended materials. Decreases in lake clarity can harm fish and aquatic plants, reduce recreational values, and increase water supply costs. Data are not adequate for national reporting on this indicator.

Biological Components

Six indicators describe the biological condition of the freshwater system. As in other systems, one tracks the native freshwater plant and animal species that are at varying levels of risk of extinction. A parallel indicator tracks the fraction of wetland and riparian (stream bank) communities—specific plant groupings—that are at risk of elimination. A third indicator tracks often unwanted non-native species, reporting now on non-native fish breeding in major watersheds but eventually including amphibians, mollusks, and plants. A fourth indicator would measure how closely fish and bottom-dwelling animal communities resemble those in relatively undisturbed lakes and streams in each region. Because abnormal environmental conditions sometimes lead to unusual animal mortality events, a fifth indicator tallies unusual mortality events among birds, fish, mammals, and amphibians (so far, data are available only for waterfowl) The final indicator will focus on measures of stream habitat quality; a companion indicator is included in the farmlands chapter.