The Oregon Department of Environmental Quality has released the 2020 Oregon Water Quality Index. The index assesses water quality at 160 ambient monitoring stations across the state. The goal is to determine the status and identify trends in waters of the state for ambient water quality conditions. The OWQI is the only water quality key performance measure reported to the Oregon Legislature. However, unlike the Integrated Report and Total Maximum Daily Load reports, the OWQI is not compared to water quality standards; does not evaluate if beneficial uses are supported; does not have regulatory standing; nor does it attempt to identify pollutant sources contributing to water quality impairments.
Each year, DEQ assigns a status to each monitoring station. Status is calculated by aggregating sub-index scores from eight parameters: temperature, pH, dissolved oxygen, biological oxygen demand, total solids, nitrate, phosphorous and bacteria. Scores range from 10 to 100 with scores of 90 and above corresponding to excellent and scores of 60 and below corresponding to very poor status.
The trends take more time to produce and can only be determined once a site has been sampled 30 or more times. Since each monitoring station is visited every two months, a site must be a part of the ambient network for a minimum of five full years before a trend can be determined.
However, inclement weather, wildfires, COVID-related travel restrictions and other safety issues may preclude a sample from being collected, thus extending the time until a trend can be determined. Trends are currently available for all 160 of the monitoring stations in the ambient network.
Key findings from this year’s OWQI include:
- The percentage of monitoring stations with excellent or good water quality remained steady at 51% from 2019.
- The number of monitoring stations that showed an improving trend in water quality also remained steady at 16% from 2019.
- The number of monitoring stations that showed a declining trend in water quality decreased from 16% in 2019 to 8% in 2020.
- The monitoring station located in the Malheur River at Little Valley showed the most improvement.
- The station showing the sharpest decline in water quality was located in Neal Creek at Fir Mountain Road in the Hood River Basin.
DEQ’s basin coordinators provided context for the changes seen across the state. Many pointed to restoration efforts, TMDLs and improvements to best management practices to control nonpoint source pollution when responding to improving trends in their basins. Stormwater runoff, agricultural impacts and the need for reduced sediment loading were identified as potential factors at sites showing declining trends in water quality.
The results of this assessment along with basin coordinator comments will be reported to the Oregon Legislature in August as a part of DEQ’s Annual Performance Progress Report.
By Dan Brown, natural resource specialist, DEQ Laboratory and Environmental Assessment Program
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