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published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution.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

The nation’s freshwater ecosystems are amazingly diverse, yet together they form an interconnected whole. They include streams and rivers, lakes and ponds, reservoirs, freshwater wetlands, groundwater, and riparian areas—the narrow strips of land along the edge of many of these bodies of water. From the Mississippi to a seasonal desert stream, from the Great Lakes to a farm pond, and from the Everglades to a prairie pothole, the nation’s fresh waters provide Americans with drinking water, food, recreational opportunities, and energy, among many other goods and services. Besides being ecosystems in their own right, freshwater systems are an essential part of every one of the other terrestrial ecosystems. Because the state of America’s waters reflects and affects the health of all other ecosystems, freshwater indicators are found throughout this report.

What can we say about the condition and use of fresh waters?

Fifteen indicators describe the condition and use of freshwater ecosystems in the United States. Partial or complete data are available for ten of these indicators. Five of these have a long enough data record from which to judge trends, and one has a federally adopted goal to use in judging current conditions. For four indicators, data are not adequate for national reporting, and one indicator requires additional development before it will be possible to assess the availability of data. In addition, indicators of nutrients and chemical contamination in fresh waters are included in every indicator chapter except Coasts and Oceans.

After the following brief summaries of the findings and data availability for each indicator, the remainder of this chapter consists of the indicators themselves. Each indicator page offers a graphic representation of the available data, defines the indicator and explains why it is important, and describes either the available data or the gaps in those data.

System Dimensions

As in each of the other systems, tracking changes in the size of the many types of freshwater ecosystems is the most basic way of describing the condition of the nation’s fresh waters. Thus our first indicator of freshwater system dimension tallies the area of lakes and wetlands and the length of streams, rivers, and riparian areas along stream banks. The second tracks the alteration of many of the elements of this complex system.

• What is the area of lakes and wetlands, and the length of streams, rivers, and their stream bank (riparian) areas? About half of all Colonial-era wetland acreage in the lower 48 states has been converted to agriculture, development, or other land uses. By the 1990s, about 10% of wetlands that had existed in the 1950s had been lost, with the rate of loss considerably lower after 1985. Lakes, reservoirs, and ponds cover about 21 million acres, and wetlands cover 94 million acres. The area of ponds (usually less than 20 acres) has increased by over 100% since the mid-1950s. This is believed to reflect the construction of small ponds, but the data do not distinguish natural from constructed ponds. More than three-fourths of streams and rivers have forests or other natural
  vegetation along their banks and riparian area. Data are not adequate for national reporting on the miles of streams of different sizes.
• How much of the nation’s lakes, wetlands, streams, and riparian areas has been significantly altered? Freshwater systems can be altered in many ways—by damming or channelizing rivers and streams, by excavating or impounding wetlands, or by converting the edge of a lake or river to a different land use, such as urban/suburban or agriculture. About one-fourth of streams and rivers have either farmlands or urban development in the narrow (about 100-foot-wide) area immediately adjacent to the water’s edge. Data are not adequate for national reporting on alterations to lakeshores or wetlands, or on streams and rivers that have been leveed, channelized, or impounded.