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 This website is no longer updated and links to external websites and some internal pages may not work.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 »

Biological Response Report

EPA’s Report, Analyzing Biological Conditions in the Animas and San Juan Rivers Following Gold King Mine Release, presents the Agency’s analysis of the effects of Gold King Mine (GKM) release on select biological organisms living in the Animas and San Juan rivers. Biological data gathered for this analysis were provided by federal, state and tribal partners in the Animas and San Juan watersheds.  After careful analysis and independent external peer review, EPA found that while some fish accumulated metals immediately after the GKM release event, levels returned to background conditions when samples were collected again the following spring. Based on the analysis of the available pre- and post-release data, EPA also concluded there were no measurable changes to fish populations and bottom-dwelling organisms after the GKM release. A scientific analysis that focuses on understanding the river conditions before the GKM release; the movement of the GKM release through the river system; and what has happened to water quality in the river since the time of the GKM release is presented in the EPA ORD Fate and Transport Report.

  • Full report (PDF) (175pp, 11M, About PDF“Analysis of the Biological Data Collected from the Animas and San Juan Rivers Following the Gold King Mine Release” 
  • Additional supporting materials and data (supporting data will become available soon; contact us for additional information).

Through the Water Infrastructure Improvements for the Nation (WIIN) Act funding provided by Congress, states and tribes continue to work collaboratively to monitor water quality throughout the San Juan Watershed.  For more information about the WIIN funded program, please visit  EPA will continue to work with states and tribes to ensure the protection of public health and the environment in the river system affected by the Gold King Mine release.