What is CADDIS?
CADDIS, or the Causal Analysis/Diagnosis Decision Information System, is an online application designed to help users conduct causal assessments, primarily in stream ecosystems. It provides a logical, step-by-step framework for Stressor Identification based on the U.S. EPA’s Stressor Identification Guidance Document, as well as additional information and tools that can be used in these assessments.
Thousands of water bodies in the United States are listed as biologically impaired. For many of these water bodies, the cause of impairment is reported as "unknown"—but before the TMDL process can be used to formulate appropriate management actions, the cause of biological impairment must be determined. Defensible causal analyses require knowledge of the mechanisms, symptoms, and stressor-response relationships for various stressors, as well as the ability to use that knowledge to draw appropriate conclusions. CADDIS was developed to provide users the information they need to conduct defensible causal assessments.
CADDIS is produced by the U.S. EPA’s Causal Analysis Team. Specific information for different sections of the site can be found on the Authors & Contributors page.
The name CADDIS is an acronym, but it also is the common name of an order of insects called caddisflies (Trichoptera). Caddisfly larvae (see illustration at right) live in flowing waters on the bottom surfaces of streams. Many species live in tubes or cases they construct from sand, pebbles, leaves, and wood, held together by an adhesive substance that the larvae secrete. They drag the case with them as they move, with only their front ends and legs sticking out. They eat algae, decaying plant matter and microorganisms, and are eaten by many types of fish. Because many caddisfly species live only in high quality streams and decrease in abundance as stream quality declines, caddisflies are one type of organism that biologists often use to monitor the health of aquatic systems.
U.S. EPA (Environmental Protection Agency). 2010. Causal Analysis/Diagnosis Decision Information System (CADDIS). Office of Research and Development, Washington, DC. Available online at https://www.epa.gov/caddis. Last updated September 23, 2010.