Marine Water

Marine water quality refers to aspects of water such as temperature, salinity, oxygen, nutrient levels, organic matter, and pH. A functioning, resilient Puget Sound ecosystem also includes marine sediment quality that supports healthy communities of sediment-dwelling invertebrates. The Marine Water Vital Sign tells us about the condition of marine waters and sediment in Puget Sound.

Marine water and sediment quality is affected by many different factors including weather, climate and circulation patterns, offshore ocean conditions, inflow from rivers and streams, discharges from wastewater treatment plants and industries, erosion and stormwater runoff, and other sources of pollution.

Deception Pass in northwest Puget Sound.

Key Vital Sign Messages

Although Puget Sound may look beautiful from the surface, marine water quality has changed in many ways. Monitoring programs document marine water quality and how Puget Sound changes over time. One challenge is gathering enough data – especially historical data – to truly understand what the ecosystem used to be like compared to now. Shifts over time in the expectations for a healthy ecosystem is referred to as “shifting baselines”. By establishing scientifically sound baselines for water quality parameters, researchers can detect changes and predict what Puget Sound will be like for future generations.

Many unknowns exist regarding Puget Sound’s future. Climate change is impacting the water cycle throughout Puget Sound, altering the seasonality and timing of key chemical, physical, and biological processes. Climate is a huge driver of marine water quality and the marine food web. As climate changes, so does the way plants and animals live in Puget Sound and how humans use Puget Sound’s resources.

  • Throughout Puget Sound, marine water quality continues to decline as shown by measures such as oxygen, temperature, pH, and nutrient balances documented in the Marine Waters 2019 Overview.
  • As the climate changes, so too does temperature and salinity. In 2019, Puget Sound waters were warmer and saltier than average – although not as warm as during the year of the “blob” of warm water from the NE Pacific Ocean. Abnormally warm and salty waters impact the Puget Sound food web; however, predicting effects on species is difficult. Warmer waters can be inhospitable to some animals (like salmon) but welcoming to other animals (like anchovy). And impacts can be complicated: warmer waters may support more abundant zooplankton populations or different types of zooplankton, which can alter food availability for fishes like Chinook salmon and Pacific herring.
  • Dissolved oxygen levels in many parts of Puget Sound were lower on average in 2019 compared to the baseline (1999–2008) conditions, continuing a six-year declining oxygen trend. The trend corresponds with anomalously warm waters (warmer water holds less oxygen). In contrast to this broader trend, certain areas (Central Basin, Quartermaster Harbor, and Bellingham Bay) reported normal to above normal oxygen – likely due to short-term effects of phytoplankton blooms or water circulation. Low oxygen waters may stress or kill fish, shellfish, and other underwater animals. In 2019, hypoxia (low oxygen) persisted from July to November in South Hood Canal, where low-oxygen areas are common at certain times of the year; luckily, no fish kills were reported.
  • Ocean acidification refers to the chemical changes that occur when the ocean’s surface absorbs excess carbon dioxide in the atmosphere. The absorption results in more acidic waters and corrosive conditions for calcifying organisms like shellfish. More acidic waters can also affect metabolic responses that control animal growth and reproduction. Ocean acidification is a continuing problem particularly in Hood Canal and the Washington coast, where carbon dioxide concentrations are higher than global averages.
  • Nitrogen is a nutrient that marine plants and animals need to grow. However, too much nitrogen can fuel algae blooms that decompose and deplete oxygen from the water. Nitrate (a form of nitrogen) in Puget Sound surface water peaked in the mid-2000s and has decreased since then. The frequency of intense phytoplankton blooms has declined while water clarity has increased since 1999. Trend patterns in nitrate, blooms and water clarity may be related to changing nutrient ratios due to changes in nutrient supply to the marine environment via weathering of feeder bluffs, loss of beach nourishment due to shoreline armoring, or changes in river flows.

Three decades of monitoring sediment chemistry, toxicity, and benthic invertebrates indicate:

  • Exposure to chemicals in sediment has generally been minimal throughout the past 20 years. Highest concentrations were near population and industrial centers; however, improvements in Elliott and Commencement Bays are noteworthy given that they are situated in more urbanized and industrial landscapes.
  • Significant declines in total abundance and taxa richness occurred in sediment-dwelling invertebrate assemblages in Puget Sound regions and bays sampled from 1997-2015. Declines occurring in invertebrate community condition despite low and declining sediment contaminant levels point to stresses from environmental pressures other than priority pollutant chemical contamination – for example, climate change, ocean acidification, and nutrient loading. 

Background Documents

Implementation Strategy

The Partnership and its affiliated network of researchers works with the three Strategic Initiative Lead Teams on Implementation Strategy development and operationalization. Please read more about these teams and our shared work at

Indicator Targets

Other Resources

Contributing Partners