[9/2007] EPA is announcing that CADDIS 2007 is available in an October 4, 2007 Federal Register Notice. To get directly to the CADDIS 2007 Application, go to


CADDIS is an on-line decision support system that helps investigators in the regions, states and tribes find, access, organize, use and share information to produce causal evaluations in aquatic systems. It is based on the US EPA's Stressor Identification process which is a formal method for identifying causes of impairments in aquatic systems.

CADDIS 2007 increases access to relevant information useful for causal analysis and provides methods and tools that practitioners can use to analyze their own data. The new Candidate Cause section provides overviews of commonly encountered causes of impairments to aquatic systems: metals, sediments, nutrients, flow alteration, temperature, ionic strength, and low dissolved oxygen. CADDIS includes new Conceptual Models that illustrate the relationships from sources to stressors to biological effects. An Interactive Conceptual Model for phosphorus links the diagram with supporting literature citations. The new Analyzing Data section helps practitioners analyze their data sets and interpret and use those results as evidence within the USEPA causal assessment process. Downloadable tools include a graphical user interface statistical package (CADStat), and programs for use with the freeware R statistical package, and a Microsoft Excel template. These tools can be used to quantify associations between causes and biological impairments using innovative methods such as species-sensitivity distributions, biological inferences, conditional probability analysis, and quantile regression analysis. New Databases have been added that provide stressor-response associations based on laboratory toxicity tests of metals and field observational data.

Image of a Caddis Fly representative of the CADDIS application

Over a thousand water bodies in the United States are listed by states as biologically impaired. For many of these, the cause of the impairment is also reported as unknown. Before an appropriate management action can be formulated, the cause of the biological impairment, for example, excess fine sediments, nutrients, or toxic substances, must be determined. Defensible causal analyses require knowledge of the mechanisms, symptoms, and stressor-response relationships for various specific stressors as well as the ability to use that knowledge to draw appropriate conclusions.

The Clean Water Act (CWA) requires that states, tribes, and territories adopt water quality standards that support designated uses including aquatic life use. These entities often measure a water body’s ability to support aquatic life by sampling fish, invertebrates, and plants. If the measurements of biological assemblages deviate from expected norms, the water body may be listed as impaired. If a water body is listed as impaired, Section 303(d) of the CWA requires states and tribes to determine the cause of the biological impairment, to calculate a level of the causal pollutant that would allow the biological condition to return to acceptable levels, and to prepare an implementation plan to achieve these objectives. A defensible process for determining cause was especially needed by resource managers when the cause is not readily apparent, or when it is necessary to convince skeptical stakeholders. The cause must be known to develop a TMDL for the right pollutant, to select among best management practices, or to develop watershed management plans. CADDIS provides an accurate and defensible process for identifying the cause of biological impairments.


CADDIS 2007 was posted to the Web site in Sept. 2007.


1998Joint ORD/OW Stressor Identification workgroup formed.
2000Stressor Identification Guidance is released. The report describes a methodology for identifying the most likely causes of observed impairments in aquatic systems. Stressor identification requires extensive knowledge of the mechanisms, symptoms, and stressor-response relationships for various specific stressors as well as the ability to use that knowledge in a formal method for causal analysis.
2002EPA host the first initial CADDIS workshop in Sterling, OH to develop a workplan for the web site.
2004EPA hosts a follow-up CADDIS development workshop in Washington, DC.
Mar 2004The CADDIS development plan is published.
Apr 2005CADDIS released for external review. [Announced in a Federal Register Notice.]
Jun 2005An external panel peer review meeting was held to review the draft CADDIS On-line Application in Washington, DC.
Jan 2006CADDIS released to the public. [Announced in a Press Release notice.]
Jan 2007The first of several modules of the CADDIS 2 revision are released for external peer review. [Announced in a Federal Register Notice.]
Mar 2007A second set of modules in the CADDIS 2007 revisions are released for an external peer review. [ Announced in a Federal Register Notice.]
Sep 2007CADDIS 2007 is released to the public. This is accounced in an October 4, 2007 Federal Register Notice.

Additional Information

CADDIS 2007 is available at