Reducing nutrients in Puget Sound

Excessive levels of nutrients, such as nitrogen, from human sources are negatively impacting Puget Sound. More than 20 years of monitoring and the Salish Sea Model show that changes in water quality, including nitrogen pollution, are increasing. Nitrogen pollution increases algae and can lead to low dissolved oxygen in the water.

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This is a serious problem for fish, animals that rely on fish such as orca, and the health of Puget Sound. Fortunately, there are solutions to this problem.

Communities can reduce the amount of excess nutrients that goes into Puget Sound and the surrounding watersheds.
We are collaborating in the Nutrient Forum with Puget Sound communities, organizations, and Tribes to find innovative and sustainable solutions.
We use the Salish Sea Model and other scientific tools to understand more about how, where, and when nutrients lead to low oxygen levels in Puget Sound.

By investing in communities and the critical wastewater infrastructure they rely on, everyone can enjoy a cleaner, healthier future for Washington's Puget Sound.

Visual shows healthy Puget Sound with diverse ecosystem and unhealthy Puget Sound. — By restoring the nutrient balance, the entire ecosystem will benefit for years to come.

Excess nutrients are a problem in Puget Sound

Too many nutrients, mainly nitrogen, result in excessive algal growth because nutrients act like fertilizer for algae and aquatic plants. When these algae and plants die, their decomposition uses up oxygen that marine animals needs to survive. This can especially be a problem in shallow inlets or bays and throws the health of Puget Sound off balance.

graphic showing 1.8 million more people will be in puget sound by 2050 and without action that is 40% increase in nutrient pollution — As the video above said, with more people comes more pee and more nitrogen pollution into Puget Sound.

Solutions for Puget Sound

Nutrient Forum meeting materials

Salish Sea Model

Wastewater treatment lagoon with blue sky in the background.

Nutrient Reduction Grant

This grant program funds planning and implementation of important upgrades at wastewater treatment facilities that reduce nutrients and help protect Puget Sound. The program’s main goal is to ease the financial burden on municipalities and support long-term nutrient management across the region. In 2025, the grant was folded into the Water Quality Combined Funding Program to allow facilities to use both nutrient reduction funding and Clean Water State Revolving Fund financing as their projects move through planning, design, and construction. Combining the programs helps meet the larger investments needed for these kinds of infrastructure upgrades.

For more information on the funding cycle, eligibility, and funding guidelines, check out the grant program webpage.

Phase 1 funding

The first phase of funding focused on nutrient monitoring, planning, and treatment process adjustments for 55 facilities discharging into Puget Sound. We funded nearly $8.75 million in nutrient reduction activities.

A few examples of upgrades that have used this funding include:

Installing or upgrading equipment to enhance the wastewater treatment process
Upgrading equipment and installing sensors that provide real-time information on nutrients and dissolved oxygen levels
Updating computer systems to monitor and control the treatment process

Phase 2 funding

Twenty-two entities will use Phase 2 funding to focus on advancing upgrades identified in planning documents, and continuing the planning work that started in Phase 1.

Nutrient Permitting

The largest source, contributing 2/3 of the excess nitrogen, is treated human waste discharged from local wastewater treatment facilities. We are using permitting to require these facilities to add nutrient-control technologies to remove excess nitrogen. View the historical information on the Puget Sound Nutrient General Permit webpage.

The state Legislature directed us to research if a nutrient credit trading program would achieve faster and more-efficient nutrient reductions for Puget Sound. Read our report that summarizes our recommendations for designing and implementing a nutrient credit trading program for facilities.

Nutrient Forum

Since 2017, we have held collaborative, public meetings called the Nutrient Forum. At the forum, we share the results from the Salish Sea Model that estimates how oxygen levels change when we reduce human nutrient inputs. We have used it to find the fewest reductions needed to get the best results for water quality. The model, along with the latest science, helps us find the right solutions for regional investments to reduce nutrient sources. See more information below about upcoming Forum meetings.

Puget Sound Nutrient Reduction Plan

Puget sound with a sailboat and people around

Draft Nutrient Reduction Plan

Based on our latest phase of modeling results, we developed the draft Puget Sound Nutrient Reduction Plan in 2025. The draft plan detailed the problem, the science, and the solutions to reduce human sources of nutrients and get to healthier oxygen levels in Puget Sound. The plan outlines approaches to get to cleaner water by 2050.

We held a public comment period from June 12 to Aug. 27, 2025. You can view all comments we received online. During this time, we held two in-person forums to share more about the draft plan and answer questions. Visit the Nutrient Forum webpage for more information, and join the Nutrient Forum email list to stay up-to-date on meetings.

Draft documents

Draft Nutrient Reduction Plan
- Appendix H - Preliminary Considerations for the Development and Implementation of Water Quality Based Effluent Limitations
Nutrient Plan focus sheet
Trading Program focus sheet

Next steps

Based on the feedback we received in 2025, we have determined we have more work to do on the Puget Sound Nutrient Reduction Plan.

Join our email list to stay up-to-date on this work.

Science and modeling

Decades of water quality monitoring data help us understand how Puget Sound water quality is changing over time. We use a robust computer modeling tool called the Salish Sea Model to study the effect of nutrient pollution on water quality and oxygen levels. We analyze and quantify nutrient impacts from sources both nearby and farther away from observed problems. The model helps us to understand the impacts of human nutrient sources and how potential source reductions could improve Puget Sound water quality. Several phases of modeling results (see below) have confirmed that human sources of nutrients are leading to dissolved oxygen problems in many parts of Puget Sound.

Optimization Scenarios Phase 2

Our latest technical report, Model Updates and Optimization Scenarios Phase 2, builds off past reports (see below) and details our approach to identify a nutrient reduction scenario that will fully restore dissolved oxygen levels in Puget Sound, as required by the Clean Water Act. The report includes the latest Salish Sea modeling results conducted in 2021-2025, a description of model updates and refinements, and results from a series of scenarios including predicted improvements to dissolved oxygen levels under hypothetical nutrient reduction scenarios. These scenarios included combinations of watershed and wastewater nutrient load reduction frameworks:

Watershed frameworks – different levels of watershed nutrient load reductions based on watershed size, location of discharge, and influence on oxygen levels in different basins, while also holding some watersheds at

Wastewater frameworks – different levels of nutrient removal from wastewater treatment plant effluent during different seasons, and based on the size and type of facility as well as the location of effluent discharge

Results of our latest modeling report demonstrate that to restore water quality in Puget Sound, wastewater treatment facilities and watersheds draining to Puget Sound will need to significantly reduce their nitrogen loading in the coming years. You can read the latest report online, download data, and we have a webmap (linked below) to view the latest modeling.

Puget Sound Nutrient Source Reduction Project – Optimization Scenarios Phase 1 is an interim analysis on the latest Salish Sea modeling results conducted 2020-2021. This technical memorandum includes results from a series of scenarios we evaluated, including predicted changes to dissolved oxygen levels due to:

Watershed nutrient reductions by region.

Wastewater treatment plant (WWTP) reductions by region.

Annual vs. seasonal treatment at WWTPs.

Future population growth projections.

Combinations of watershed and WWTP reductions.

Our blog post, Nutrient pollution modeling shows different futures for Puget Sound, offers a high-level overview of this study, and you can also view model results on the Optimization Scenarios Phase 1 webmap. Tech memo appendices are posted on the Nutrient Forum webpage.

Puget Sound Nutrient Source Reduction Project Volume 1: Model Updates and Bounding Scenarios, or the Bounding Scenarios report, evaluated changes to dissolved oxygen levels when modeling reductions in nitrogen and carbon at municipal wastewater treatment plants. 

The Salish Sea Model study confirmed that human sources of nutrients have a significant impact on dissolved oxygen in Puget Sound. This assessment concluded that reducing nutrient pollution at municipal wastewater treatment plants would provide significant progress toward meeting dissolved oxygen water quality standards in the sound.

Our published Salish Sea modeling results inform future actions for protecting Puget Sound. You may directly download model outputs and data and view all Salish Sea Model publications. 

Our previous reports detail the model scenarios we have run to estimate the amount of excess nutrients coming from different sources (called nutrient loads), understand human’s contributions to those loads, and understand the impact of those loads on dissolved oxygen levels throughout the Sound.

Salish Sea Model web map

Nitrogen sources

keyboard with download symbol highlighted

Download Salish Sea Model files

Frequently Asked Questions

This draft plan does not have permit limits in it. The modeling done to help understand the benefits of different nutrient reduction efforts does not directly equate to permit limits for wastewater treatment plants and industrial dischargers in Puget Sound. Instead, the plan sets basin wide targets that our permit writers will then use to translate into water quality based effluent limits in permits.

As outlined in the draft plan, improving the nutrient controls at many wastewater treatment plants is critical to solving this problem. For many facilities, this will mean new permitting requirements from Ecology triggering the need for long term planning and investment in nutrient control technologies.

Ecology plans to convene a technical advisory committee to guide its approach to developing nitrogen limits and incorporating them into future permit updates. Further information on approaches to developing permit limits and the technical advisory committee is available as part of the draft plan.

Yes. The Pacific Ocean is the largest natural source of nitrogen to Puget Sound, but a majority of this nitrogen entering Puget Sound from the ocean does not stay in the surface waters and instead flows back out to the coast.

Our modeling results show that excess nutrients from local human sources are contributing to low levels of dissolved oxygen. These oxygen levels are lower than those influenced by natural sources alone and the impact from human sources is more than is allowed by state water quality standards.

To learn more about nitrogen sources to Puget Sound, view our Nitrogen in Puget Sound Storymap.

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Los niveles excesivos de nutrientes provenientes de fuentes humanas, como nitrógeno y carbono, están afectando la calidad del agua en Puget Sound. Demasiados nutrientes en el agua actúan como fertilizante y causan el crecimiento excesivo de algas y plantas acuáticas. Cuando esas algas y plantas mueren, su descomposición utiliza el oxígeno que los animales marinos necesitan para sobrevivir. Esto puede ser un problema especialmente en ensenadas poco profundas o bahías y desequilibra la salud de Puget Sound.

Ecología está colaborando con Tribus y la comunidad de Puget Sound a través del Programa de Reducción de Nutrientes de Puget Sound (en inglés) para encontrar soluciones que reduzcan otras fuentes humanas que resultan en un exceso de nutrientes. También estamos implementando el Permiso General de Nutrientes de Puget Sound (en inglés) para las plantas de tratamiento de aguas residuales, que abordará la mayor fuente de exceso de nutrientes que ingresan a Puget Sound.

Las fuentes humanas de nutrientes incluyen:

Las aguas residuales descargadas de las plantas de tratamiento.
Uso excesivo de fertilizante, que ingresa a las vías fluviales cuando llueve.
Mala gestión de la tierra, especialmente la relacionada con ganado.
Sistemas sépticos en el sitio.

Además de niveles bajos de oxígeno, los efectos del exceso de nutrientes incluyen:

Acidificación del agua, lo cual impide que los mariscos y otros organismos formen conchas.
Cambios en el número y los tipos de organismos que viven en el fondo del mar, lo cual cambia la red alimentaria.
Aumento en el crecimiento de macroalgas, que afecta la salud de la zostera marina y los lechos de mariscos.
Aumento de la proliferación de algas y alteración a corto plazo de la cadena alimentaria como consecuencia del aumento de ciertas especies, como las medusas.

Para obtener más información, llame a Jeremy Reiman al 360-819-0197 y solicite un intérprete.

We offer free language services about our programs and services for people whose primary language is not English. We can provide written information in your preferred language and interpreters in person or over the telephone.

Contact our Language Access team: language@ecy.wa.gov

Contact information

Ben Rau
Watershed Planning Unit Manager
Ben.Rau@ecy.wa.gov
360-742-6529