The Clean Water Act, Biological Integrity, and Stressor IdentificationEdit

Since the inception of the Clean Water Act (CWA) in 1972, the rivers, lakes, estuaries, and wetlands of the United States have indeed become cleaner. The standard for measuring these improvements are both chemical and biological. Yet, we know that many waterbodies still fail to meet the goal of the Clean Water Act – to maintain the chemical, physical and biological integrity of the nation's waters.

Biological assessments have become increasingly important tools for managing water quality to meet the goals of the CWA. These methods, which use measurements of aquatic biological communities, are particularly important for evaluating the impacts of chemicals for which there are no water quality standards, and for non-chemical stressors such as flow alteration, siltation, and invasive species. However, although biological assessments are critical tools for detecting impairment, they do not identify the cause or causes of the impairment.

The Office of Water (EPA) and Office of Research and Development (EPA of the US EPA have developed a process for identifying any type of stressor or combination of stressors that cause biological impairment. The Stressor Identification (SI) Guidance is intended to lead water resource managers through a formal and rigorous process that

  • identifies stressors causing biological impairment in aquatic ecosystems, and
  • provides a structure for organizing the scientific evidence supporting the


The ability to accurately identify stressors and defend the evidence supporting those findings is a critical step in developing strategies that will improve the quality of aquatic resources.

The Stressor Identification process (SI) is prompted by biological assessment data indicating that a biological impairment has occurred. The general SI process entails critically reviewing available information, forming possible stressor scenarios that might explain the impairment, analyzing those scenarios, and producing conclusions about which stressor or stressors are causing the impairment. The SI process is iterative, usually beginning with a retrospective analysis of available data. The accuracy of the identification depends on the quality of data and other information used in the SI process. In some cases, additional data collection may be necessary to accurately identify the stressor(s). The conclusions can be translated into management actions and the effectiveness of those management actions can be monitored.

The foregoing is copyrighted material from the first section of the Executive summary, page 16 of Stressor Identification Guidance Document Office of Water (EPA) and Office of Research and Development (EPA EPA-822-B-00-025, a document produced by employees of the government of the United States in the course of their employment, thus in the public domain. It may be edited, but the jargon used should not be removed.

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