The Oregon Department of Environmental Quality has released the 2021 Oregon Water Quality Index. It 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 or the Water Quality Status and Trends Report, 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. Results 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. We created a story map providing more details on the various sub-indices you can find here.
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 part of the ambient network for a minimum of five full years before a trend can be determined. However, inclement weather, wildfires 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 159 of the 160 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 dropped slightly to 49% in 2021.
- The number of monitoring stations that showed an improving trend in water quality also dropped to 8% in 2021.
- The number of monitoring stations that showed a declining trend in water quality increased to 11% in 2021.
- Total solids, dissolved oxygen and nitrogen had the highest percentage of declining sub-index trends while temperature had the highest percentage of improving sub-index trends.
- More than 60% of sites in the agriculture, range and urban land use types had status of fair to very poor for the fourth consecutive year.
- The average improving trend magnitude was higher at sites in fair to very poor status than at sites in good or excellent status, indicating that the largest gains in water quality occurred at sites most in need of improvement.
DEQ’s basin coordinators provided context for the changes seen across the state. Many pointed to restoration efforts by watershed councils and soil and water conservation districts, improvements to irrigation systems and best management practices to control nonpoint source pollution when responding to improving trends in their basins. However, lack of riparian buffers, wildfire impacts, cattle grazing, old septic systems, untreated stormwater discharges and lack of resources to upgrade water treatment services 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. The data is also incorporated into the Integrated Report, which indicates impaired waters to EPA and helps prioritize waters in need of further evaluation.
By Dan Brown, natural resource specialist, DEQ Laboratory and Environmental Assessment Program