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Assessment Methodology Updates

EPA regulations require states to describe the methodology, data and information used to identify and list water quality limited segments requiring TMDLs. 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 may update the existing assessment methodology and develop new methodologies. Oregon statute requires that DEQ publish the Integrated Report assessment methodology prior to the start of drafting the Integrated Report. DEQ has set a strategic vision for the Water Quality Assessment program composed of short-term and long-term priorities. 

2024 Integrated Report cycle methodology updates

The Assessment Methodology for Oregon's 2024 Integrated Report Cycle will include updates for inland, estuary and marine waters.

Currently, the draft 2024 Assessment Methodology Document includes only inland and estuarian waters. DEQ plans to release new marine water methodologies for assessing impacts of ocean acidification and hypoxia for public comment in May 2023. DEQ will release a response to comment document on the methodology prior to the release of the draft Integrated Report.

Marine waters - 2024 updates

DEQ is working with a scientific technical workgroup to draft methodologies for assessing the impacts of ocean acidification and marine dissolved oxygen in Oregon's territorial waters for use in the 2024 assessment.

Public process

Request for comments

DEQ plans to request comments on draft methodologies for assessing impacts of ocean acidification and hypoxia in May 2023. The draft methodologies will be accompanied by a technical support document detailing DEQ's proposed rationale and process. A public webinar will be held after the release of these documents.

Marine data call for data

DEQ plans to hold an open call for marine data from Jun. 15, 2023 through Aug. 14, 2023, for a total of 60 days. DEQ does not expect to extend the data solicitation deadline. 

Visit the Call for Data web page for information about data submission templates, video tutorials and submission guidelines. 

Notifications about the public comment period and marine call for data will be distributed via DEQ's GovDelivery subscription service.

In the 2024 Integrated Report Cycle, DEQ completed the following updates to the Assessment Methodology for inland and estuary waters:

Public process

Request for comments

The public comment period for the Draft Assessment Methodology (for inland and estuarine waters) for Oregon's 2024 Integrated Report was open from Jan. 5, 2023, through Feb. 21, 2023, for a total of 47 days.

Assessment methodology webinar

DEQ provided a webinar on Jan. 12, 2023 for the use of the 2022 Integrated Report tools and 2024 methodology updates. 

Call for data

DEQ's call for data (for inland and estuarine waters) was open from Feb. 6, 2023 through April 7, 2023, for a total of 60 days.​​

Future Integrated Report cycle 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 WQ program goals.

Freshwater biocriteria

​​DEQ is committed to making updates to the biocriteria methodology based on peer review recommendations received in 2018. DEQ has updated its reference screening protocols, identified additional reference site data, and incorporated new data into its reference screening process. DEQ is exploring the option of a new or revised model, multi-metric index, and additional supporting lines of evidence. This work fulfills DEQ's commitment to EPA to pursue additional steps and lines of evidence to increase confidence in DEQ's interpretation of its biocriteria narrative.​

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 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(2)). ​

​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.


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.


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. ​