Freshwater Quality

Freshwater quality refers to many aspects of water in rivers and streams including dissolved oxygen, pH, temperature, bacteria, nitrogen, phosphorus, suspended sediment, and turbidity. Freshwater quality throughout Puget Sound is affected by many different factors including weather and climate patterns, water withdrawals and diversions, erosion and stormwater runoff, discharges from wastewater treatment plants and industries, nutrient input and other pollution. This Vital Sign tells us about the condition of the fresh water that is vital to people, fish and wildlife populations by monitoring trends in water quality and ecological function of rivers and streams in Puget Sound.


Key Vital Sign Messages

  •       Caddisfly larva in its casing (Limnephilidae)
    Streams, rivers, or lakes are considered impaired when they fail to meet water quality standards for bacteria, dissolved oxygen, temperature, toxics, or other pollutants. Once a waterbody is listed as impaired, a plan must be created and implemented to control pollution or improve water quality (see the Department of Ecology Total Maximum Daily Load process).
  • Since 1988, impairment of water quality has been assessed in approximately 10 percent of the waters of Washington State. In the Department of Ecology’s 2014 water quality assessment, 1,694 listings were deemed impaired, amounting to hundreds of water bodies not meeting state standards. Of the 2,071 sites that were assessed in both 2004 and 2014, 3 percent improved from ‘impaired’ to ‘non-impaired’ (healthy), mostly due to the successful implementation of pollution control practices including efforts to reduce fecal bacteria pollution. Unfortunately, 19 percent of the assessed waterbodies status changed to ‘impaired’, and the majority of listings were unchanged and remained impaired (41 percent).
  • Overall freshwater quality, as measured by the Water Quality Index, has not changed substantially since 1997 at the 31 river and stream monitoring stations across Puget Sound watersheds. However, WQI scores do demonstrate improvements in measures of fecal coliform bacteria and total nitrogen for major rivers in Puget Sound.
  • On average, between 2013 and 2017, only one-third of the monitoring stations had a Water Quality Index score indicating good stream health. While improvements have been observed in two river systems, the Nisqually River and Deschutes River, the slow rate of progress in overall water quality trends suggests the recovery target is not likely to be reached by 2020.
  • The Benthic Index of Biotic Integrity (B-IBI) uses the diversity and abundance of invertebrates to measure stream health. Comparing B-IBI scores at stream sites across Puget Sound between two time periods (2006-2009 and 2015-2018) showed that while some sites that were in excellent condition declined to good or fair, overall more sites improved in condition than declined.
  • Stormwater runoff from urban and urbanizing areas causes the majority of habitat and water quality degradation in small streams.
  • The Stormwater Action Monitoring program is a collaborative, regional monitoring program intended to assess biological condition of instream and riparian habitat in Puget Sound streams and provide advice on improving stormwater management and protecting beneficial uses (DeGasperi et al. 2018). A 2015 assessment of conditions within and outside Urban Growth Areas (UGAs) found B-IBI scores to be significantly better outside UGAs (69 percent of stream length in good or fair condition) compared to within UGAs (82 percent of stream length in poor condition) (DeGasperi et al. 2018).
  • The B-IBI Interdisciplinary Team, the group leading development of the B-IBI Implementation Strategy, identified priority strategies to address the effects to stream health from the built environment and effects from the runoff of working lands, and strategies to protect heathy streams from the impacts of new development.

Strategies, Actions, and Effectiveness

Other Resources

Contributing Partners



Mary Ramirez and Leska Fore, Puget Sound Partnership
Last Updated