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Oregon Water Quality Index

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Links to OWQI Reports and Methods

How The OWQI Gets Used



The Oregon Water Quality Index (OWQI) analyzes a defined set of water quality variables and produces a score describing general water quality. The water quality variables included in the OWQI are temperature, dissolved oxygen (percent saturation and concentration), biochemical oxygen demand, pH, total solids, ammonia and nitrate nitrogen, total phosphorus, and bacteria. The OWQI transforms raw data into unitless subindex values which are aggregated to generate an overall score for a particular monitoring site. Scores range from 10 (worst case) to 100 (ideal water quality). These subindices are combined to give a single water quality index value ranging from 10 to 100. The unweighted harmonic square mean formula used to combine subindices allows the most impacted parameter to impart the greatest influence on the water quality index. This method acknowledges that different water quality parameters will pose differing significance to overall water quality at different times and locations. The formula is sensitive to changing conditions and to significant impacts on water quality. Data from the Large River Ambient Monitoring Program is used for these analyses. The index does not consider changes in toxics concentrations, habitat, or biology. In addition, it is not possible to make inferences of water quality conditions outside of the actual ambient network site locations.

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For more information about DEQ's Laboratory and Environmental Assessment Division please email LEAD.


Oregon Department of Environmental Quality
Headquarters: 811 SW Sixth Ave., Portland, OR 97204-1390
Phone: 503-229-5696 or toll free in Oregon 1-800-452-4011
Oregon Telecommunications Relay Service: 1-800-735-2900  FAX: 503-229-6124

The Oregon Department of Environmental Quality is a regulatory agency authorized to protect Oregon's environment by
the State of Oregon and the Environmental Protection Agency.

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