DEQ updates interactive map of Oregon’s water quality

The Oregon Department of Environmental Quality has released the 2019 Oregon Water Quality Index. The index, or OWQI, details water quality assessments at 160 ambient monitoring stations across the state.

The goal of this assessment is to determine the status of state waters and identify trends in water quality. The Oregon Legislature relies on the OWQI to measure water quality performance.

Each year, DEQ staff assign a status to each monitoring station based on data from the most recent water year (October 1-September 30). The status is calculated by combining scores from eight categories: 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.

Trends take 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 and other safety issues may preclude a sample from being collected, extending the time until a trend can be determined. Trends are currently available for 152 of the 160 monitoring stations.

The key findings from this year’s OWQI include:

• The percentage of monitoring stations with excellent or good water quality remained steady at 51% from 2018.
• The number of monitoring stations that showed an improving trend in water quality dropped from 30% in 2018 to 16% in 2019.
• The number of monitoring stations that showed a declining trend in water quality increased from 9% in 2018 to 16% in 2019.
• Rhea Creek at Morter Road was the monitoring station showing the most improvement with a positive trend of 8.1 magnitude.
• The station showing the sharpest decline (-5.9 magnitude) was the South Fork Coquille at Broadbent.

Basin coordinators provided context for the changes seen across the state. Many pointed to collaborations and partnerships as well as Total Maximum Daily Loads, the maximum amount of a pollutant allowed in a waterbody, and improvements to best management practices in agricultural lands when responding to improving trends in their basins. While dam operations, harmful algal blooms, agricultural impacts and crop rotations, along with the need for reduction in sediment loading were all 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 Legislature in August as a part of the Annual Performance Progress Report.

— Dan Brown, DEQ water quality resource specialist