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Nutrients in Puget Sound
King County invests in water quality monitoring and analysis to better understand how excess nitrogen affects marine life. This is part of a shared commitment to protect Puget Sound marine life.
A shared commitment to protecting Puget Sound marine life
Our steadfast commitment to protecting Puget Sound includes doing our part to ensure there is enough oxygen available for marine life.
Too much nitrogen – a naturally occurring nutrient that is the building block of life on land and in the sea – can lower the levels of oxygen in some areas of Puget Sound. An estimated 91 percent of nitrogen in Puget Sound comes from natural sources – mostly flowing in from the Pacific Ocean – while 9 percent comes from human activity that includes wastewater discharges, on-site septic systems, and agricultural runoff.
We comply with regulations issued by the Washington Department of Ecology to hold the amount of nitrogen discharged by the County’s wastewater treatment plants steady while we plan for future treatment options and study the effectiveness of our actions.
We have expanded our water quality monitoring program to include the Whidbey Basin, where Ecology’s scientific model identifies an area potentially affected by nutrients discharged by King County’s wastewater treatment system.
We are investing in monitoring and analysis in partnership with Tribes and universities to better understand localized dynamics of nutrients and dissolved oxygen in shallow bays and how excess nitrogen impacts marine life. We are reviewing trends in nutrients and blooms of phytoplankton over time, providing information that can inform decisions and help produce the best results for aquatic life.
The Puget Sound Nutrient General Permit issued by the Washington Department of Ecology directs us to optimize how our wastewater treatment plants address nitrogen today and assess future technology and cost of different options to further reduce nitrogen with additional infrastructure upgrades. The cost analysis includes assessment of utility rate increases and the effect on household affordability.
In the meantime, we will continue to protect Puget Sound by enhancing our wastewater system to make it safer, more reliable, and more resilient to climate impacts. That is in addition to our investments in stormwater management, land conservation, enforcement of on-site septic system requirements, and work to improve streamside corridors to help reduce other nutrient inputs to Puget Sound.
Answers to frequently asked questions
A: Much like in a garden, nitrogen combined with sunlight can stimulate plant growth in marine waters. However, excess nitrogen can lead to larger algal blooms. When the algae die, the decomposition process consumes oxygen, lowering the levels of oxygen available for marine life in Puget Sound.
A: An estimated 91 percent of nitrogen in Puget Sound comes from natural sources, mostly flowing in from the Pacific Ocean. The remaining 9 percent comes from human sources that include wastewater effluent as well as urban stormwater and agricultural runoff.
A: Our regional treatment system does a great job treating for pathogens and other contaminants, however, it was not designed or built to address nitrogen.
Through minor adjustments to our existing treatment processes, we’ve been able to keep nitrogen levels steady with existing infrastructure even as our region’s population grows and the amount of nitrogen entering our system increases. In the meantime, we’re studying options for future treatment upgrades that will further reduce nitrogen. This study is assessing treatment technologies, implementation schedules, and financing and impacts to household affordability and will be completed at the end of 2025.