Skip to main content

Oregon State Flag An official website of the State of Oregon »

Assessment Methodology Updates

U.S. Environmental Protection Agency regulations require states to describe the methodology, data and information used for their integrated report, a comprehensive evaluation of Oregon’s surface waters. Specifically, it helps DEQ to identify and list water quality limited segments requiring TMDL clean water plans. Oregon's assessment methodology contains the "decision rules" DEQ uses to compare data and information to existing water quality standards to develop the biennial Integrated Report pursuant to Clean Water Act Sections 303(d) and 305(b) and OAR 340-041-0046. The methodology builds on DEQ's protocols from previous 305(b)/303(d) assessments. 

Before each reporting cycle, DEQ updates the assessment methodology to revise existing and develop new methods. Oregon statute requires that DEQ publish the Integrated Report assessment methodology prior to the start of drafting the Integrated Report.

2026 Integrated Report cycle methodology updates

In the 2026 Integrated Report cycle, DEQ completes the following updates to the assessment methodology:

These updates, and the rest of the assessment methodology can be found in the Draft 2026 Assessment Methodology

Public involvement

Assessment methodology comment period

You can comment now on DEQ's proposed methodology for developing the 2026 Integrated Report, officially referred to as the Draft Assessment Methodology. The public comment period is open from March 25, 2025 to May 27, 2025. DEQ does not expect to extend the comment deadline in order to meet the federal reporting schedule. 

Please submit comments to: integratedreport@deq.oregon.gov


Assessment Methodology Webinar

DEQ will host a public webinar on April 2, 2025 from 1 p.m. to 3 p.m. to provide more information about the technical aspects of the assessment methodology. 

Sign up for the webinar.
After registering, you will receive a confirmation email containing information about joining the meeting.

Call for data submissions 

DEQ's is also asking for data submissions to consider as part of the 2026 Integrated Report process. This call for data is open. Please see the Call for Data web page for more information, including data submission templates. 

Future Integrated Report updates

DEQ has set a strategic vision for the water quality assessment program composed of short-term and long-term priorities. Short-term updates will be taken on in the next two assessment cycles. Long-term updates will be developed in coordination with water quality program goals.

Tissue toxics

Oregon's methodology for listing segments of waterbodies as “impaired" for toxics does not currently include a method for assessing toxics data in tissue other than for mercury. Category 5 listings are based on either water column concentrations of toxic pollutants, or on fish advisories issued by the Oregon Health Authority. DEQ is developing a method to assess support of the fish consumption (fishing) beneficial use using data collected from aquatic tissue samples by interpreting Oregon's narrative criteria for toxic substances OAR 340-041-0033(1).

Using benchmarks to assess toxics narrative criteria

DEQ will evaluate the use of guidance values, or concentrations for toxic compounds that do not have WQ criteria that DEQ may use in application of Oregon's Toxic Substances Narrative (340-041-0033(1)).  ​


​​Aquatic weeds

​​​The current assessment method of the Narrative Criteria ORS 340-041-0007(9) lacks specific details and protocols. To support a determination of impairment by aquatic weeds or algae, terms such as “excessive growths” and “dominate the assemblage” must be clarified and a weight of evidence approach defined. This update will add clarity to the existing methodology.

Excessive algae

​​DEQ historically listed waterbodies based on excessive amounts of algae (i.e. benthic/floating algae). DEQ is exploring multiple lines of evidence that may be used to assess attainment of this criteria. This update will provide clarity and a clear weight of evidence approach to remove “excessive algae” listings. Lines of evidence may include: methods for visual estimation of algae, periphyton biomass thresholds, algae community composition, and other supporting WQ information such as nutrients, diel dissolved oxygen and/or pH.

Nutrients

In conjunction with protocols for excessive algae, DEQ plan to develop a weight of evidence approach for nutrient impairment.  Possible lines of evidence could be diel DO/pH, phosphorus/nitrogen concentrations together with chlorophyll (water column and benthic), phytoplankton community structure, and macroinvertebrates.​

Assessment of TMDL benchmarks for Category 2

​​​DEQ is coordinating with EPA to determine, where no numeric criteria exist (i.e. phosphorus, nutrients, sediment), whether attainment of TMDL targets/benchmarks may be used to identify where waterbodies have been restored and beneficial uses are currently being supported.

Sediment

Sedimentation is a significant cause of impaired waters in Oregon.  Development of a sedimentation benchmark and corresponding assessment methodology would require peer review. A methodology to assess suspended and bedded sediment would build on current knowledge and procedures for implementing the narrative criterion. ​