News Releases

Corps confirms localized sediment contamination in Big Cliff Reservoir

Published June 28, 2019
Map of Big Cliff Remediation Site

Map of Big Cliff Remediation Site

PORTLAND, Ore. - The U.S. Army Corps of Engineers recently completed a Remedial Investigation in Big Cliff Reservoir and confirmed localized sediment contamination in one area of the reservoir.

At this time, the Corps determined that there may be potential risk to human health in cases of repeated and long-term direct contact with the localized contaminated sediments or consumption of resident (non-migratory) aquatic life.

The Corps advises members of the public to avoid consuming fish and other aquatic life from Big Cliff Reservoir, and to avoid engaging in any activity in the reservoir that may disturb sediments (e.g., wading in low water, swimming, diving, creating prop wash, dragging anchors, digging, etc.) while the Corps continues the investigation. The Corps is posting signs on site at Big Cliff Reservoir to alert members of the public.

The Corps’ risk assessment found contaminant concentrations above Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) limits for two specific groups, outlined in the following scenarios:

  • People who eat resident fish at amounts equivalent to a portion of fish once a week, every week, for 20 years (for adults) or 6 years (for children);
  • Children who play in the localized sediment area at a frequency equivalent to twice a week, for 6 months, over 6 years (52 days a year for 6 years).

The Corps’ risk assessment showed acceptable levels (i.e., within CERCLA thresholds) for the following scenarios:

  • Adults recreating at Big Cliff;
  • Children recreating at a frequency equivalent to once a week, compared to twice a week (26 days a year for 6 years);
  • People consuming resident fish at a rate equivalent to one portion, every other week, compared to every week.

CERCLA sets thresholds for increased health risks. When contaminant levels are above CERCLA thresholds, federal action is required to reduce exposure to site contaminants.

Water sampling results show reservoir water is not impacted by this localized sediment contamination. Water samples were collected in both low-flow and high-flow conditions.  Contaminant concentrations in reservoir water from the site were either below screening levels or similar to upstream reference locations.

During the next portion of the investigation, the Corps will test reservoir organisms like resident fish, and crawfish, to see if they have been impacted.

Detroit Reservoir is not impacted by this contamination. The Corps encourages the public to make use of the many recreation areas managed by the Oregon Parks and Recreation Department and the U.S. Forest Service around Detroit Reservoir, about four miles upriver from Big Cliff Dam.

Public health and safety is the Corps’ priority. The Corps is taking additional steps to better understand these risks and will continue to conduct studies to further understand the potential impacts of the contamination. The Corps expects to make the results of the fish tissue analysis available toward the end of 2019. The Corps will provide results to regulatory agencies and update the public as soon as the results are available.  

For more information, visit or call 503-808-4510.

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Lauren Bennett

Release no. 19-013

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