An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

CADDIS Volume 1

Figure: Mechanistically Plausible Cause

Figure 4-4. Mechanistically Plausible Cause

This illustration shows that if the impairment is a fish kill with dermal lesions, then the candidate cause "copper toxicity" is not mechanistically plausible, because copper does not cause dermal lesions.

                     Fig 4-4 illustrates 2 dead fish from exposure to an impairment like copper toxicity.Figure 4.4 Mechanistically Plausible Cause. This illustration shows a fish kill with dermal lesions.

Top of Page

Explanation of the Types of Evidence Illustrations

This description applies to each of the types of evidence illustrations. These illustrations provide graphic explanations of the types of evidence. They are somewhat abstract to convey that they are representative of the concept rather than illustrations of particular applications. The live fish (green and upright) represent unimpaired organisms, populations or communities of all types, not just fish. The dead fish (white and belly-up at the surface) represent all biological impairments, not just dead fish. The pipe represents all sources and the yellow effluent plume represents all causal agents (stressors), not just effluents or even chemicals. Clock faces represent the passage of time, not the particular time difference illustrated. Fish in beakers represent laboratory tests. Other graphic elements used in particular illustrations are explained in the caption.

Top of Page