Library Index » Science Encyclopedia » Surface Water: Rivers and Lakes - Characteristics Of Rivers And Lakes, The Need For Pollution Control, Assessing Water Quality, Water Quality Of The Nation's Riversand Streams

Surface Water: Rivers and Lakes - Assessing Water Quality

body pollutants data source

Defining water quality is a little like trying to determine "how clean is clean?" Currently, the best measure is the degree to which a water body is capable of supporting its designated uses.

State 305(b) Reports

Because of funding limitations, most states assess only a portion of their total water resources during each CWA-required two-year reporting cycle. The goal is to rotate the sites that are assessed in each cycle so that over a five-year period all waters are assessed. In the 2000 National Water Quality Inventory, the states evaluated about 19% of the nation's river and stream miles and about 43% of lake, pond, and reservoir acres. State data for 2002 has been reported to the EPA, but this information had not yet been consolidated into a national report as of mid-2005.

The states use chemical and biological monitoring results and other types of data, such as water-quality models, surveys of fisheries, and information from citizens, to evaluate their water quality. The data are compared with the water-quality criteria adopted to protect each use designated for a particular water body, and water bodies are rated as to how they meet their uses. Every two years the results of these evaluations are reported to the EPA in each state's 305(b) report.

Because of sparse reporting by the states and differences in criteria and measurement techniques between states, a completely accurate assessment of the quality of the nation's surface waters is not yet possible. The reports, however, are valuable as a measure of estimated overall water quality and as a means of identifying the major sources and causes of pollution.

States use two categories of data to assess water quality. The first and best category is monitored data. Monitored data are field measurements of biological, habitat, toxicity, physical, and chemical conditions in water, sediment, and fish tissue. These data are gathered at least every five years. The second category, used to fill information gaps, is evaluated data, which include field measurements more than five years old and estimates that are generated using land-use and pollution-source information, predictive models, and surveys of fish and game. These data can provide an indicator of water quality, but because they vary in quality and confidence, their use is limited.

Index of Watershed Indicators

Reporting the health of the nation's aquatic resources is more difficult than reporting water quality. To meet this challenge, the EPA, the states, and their many public and private partners have developed the Index of Watershed Indicators (IWI). IWI looks at a variety of "indicators" that point to whether rivers, lakes, streams, wetlands, and coastal areas are "well" or "ailing," and whether the activities taking place on surrounding lands are placing them at risk. The objective is to establish a national baseline on the condition and vulnerability of aquatic resources—a baseline that can be used, over time, to help measure progress toward the goal that all water-sheds be healthy and productive places. In Index of Watershed Indicators: An Overview (EPA, August 2002), the following watershed conditions were reported:

  • 15% of the nation's watersheds had relatively good water quality.
  • 36% had moderate problems.
  • 22% of the watersheds had more serious water-quality problems.
  • 27% did not have enough information to be characterized.

The report also revealed that one in fifteen water-sheds nationally was highly vulnerable to further degradation.

Point and Nonpoint Sources of Pollution

Pollutants enter a body of water in any number of ways. Pollutant sources can be divided into two major types: point and nonpoint. Point sources are those that disperse pollutants from a specific source or area, such as FIGURE 3.3
Activities within a watershed that can contribute to nonpoint source pollution
SOURCE: "Activities within a Watershed That Can Contribute to Nonpoint Source Pollution," in Water Quality: Federal Role in Addressing—and Contributing to—Nonpoint Source Pollution, U.S. General Accounting Office, 1999
a wastewater treatment plant discharge. Pollutants that are commonly discharged from point sources include bacteria, toxic and nontoxic chemicals, nutrients, and heavy metals from industrial plants.

Nonpoint sources are those that are spread out over a large area and have no specific outlet or discharge point. For example, agricultural and urban runoff; runoff from mining and construction sites; and accidental spills, as when a train or truck carrying toxic chemicals derails or overturns, releasing its contents. Nonpoint source pollutants can include bacteria from cat and dog wastes, pesticides, fertilizers, toxic chemicals, and salts from road construction. (Figure 3.3 shows activities that can contribute to nonpoint pollution.)

The designated use of a water body is "impaired" when the amount of pollutant in that water body reaches the level where the water cannot meet the water-quality criteria for its designated use or uses. This does not necessarily mean that the water body is badly degraded. For example, a stream may exceed the water-quality criteria for temperature established to protect a cold-water fish such as trout and still support an active trout fishery. The "impairment" may be only slightly in excess of water-quality criteria. A water body can be impaired for one designated use and still fully support other designated uses. For example, a lake may have a thriving recreational fishery but be unsafe for swimming because of high bacteria levels in the water, thereby meeting the "fishable" designation but not the "swimmable" designation. In other cases, impairment may be so bad that one or more uses are lost. An example would be a lake that has been choked by noxious weeds from excessive nutrients, resulting in fishkills and severely reduced fish populations, leading to the loss of an active recreational fishery.

Where impaired conditions are deemed irreversible, the water quality is determined to be unattainable. To reach this determination, the states perform a use-attainability analysis to show that one or more designated uses cannot be supported because of biological, physical, chemical, or economic/social conditions. Examples of conditions that might result in a determination that a use is not attainable include low flow, naturally occurring high levels of pollutants, or the presence of dams or other hydrologic modifications that permanently alter water body characteristics.

Managing Water Quality

Once states have determined that a specific water body does not meet the water-quality criteria needed to protect its designated uses, they begin the process of determining what actions are necessary to restore water quality. The first step is to identify the total maximum daily load (TMDL) for each pollutant. The TMDL is the maximum amount of a pollutant that a water body can receive on a periodic basis and still support its intended uses. TMDLs are generally developed by identifying the pollutants and the source of the pollutants causing a water-quality problem, and determining how much the pollutants need to be reduced in order to enable the water body to meet the water-quality standards. Reductions in pollutants are then achieved through limits in discharge permits, requirements for best management practices, and other regulatory or voluntary practices.

Surface Water: Rivers and Lakes - Water Quality Of The Nation's Riversand Streams [next] [back] Surface Water: Rivers and Lakes - The Need For Pollution Control

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