Dissolved oxygen in marine water:  Low oxygen waters may stress or kill fish and shellfish, or reduce food availability for birds and marine mammals. Waters with low dissolved oxygen are naturally present in Puget Sound and can result from low oxygen waters entering the Salish Sea from the ocean, changes in river flow, or lack of vertical mixing.  

Marine benthic communities: The areas where bottom-dwelling benthic communities are impacted by natural and human-caused pressures are expanding. Excessive amounts of organic material reaching the sediments account for much of the human disturbance to benthic communities, especially in inlets with low tidal exchange.    

Marine water temperature: Warmer waters can change species found in Puget Sound and impact the food web by changing shellfish spawn time, reducing nutritional value of zooplankton, and slowing kelp growth. Puget Sound waters have been seasonally warmer than average, which can be driven by regional climate events such as El Niño, Pacific marine heatwaves, and shifting weather patterns.   

Nutrient balance in marine water:  Puget Sound nutrients vary on multidecadal and shorter time scales. Over the last decade nutrients have been higher than average and increasing in some areas, and lower than average and decreasing in others. The mechanism of the cyclical behavior of nutrients in Puget Sound is currently not fully understood. 

Ocean acidification:  Ocean acidification is an increasing threat to Puget Sound as estuarine processes, both natural and human-caused, can also lower the pH of marine waters. Coastal upwelling brings deeper, lower pH ocean waters into Puget Sound. Puget Sound waters are particularly sensitive to these conditions.  

Primary production in marine water:  Marine phytoplankton abundance and timing of blooms has been variable from year to year. This is especially true in recent years where climate anomalies have affected water properties that influence phytoplankton. Similarly, species composition has also been variable from year to year and can have ripple effects throughout the food web.  

Sediment chemistry:  Chemical contamination in sediment has generally been stable throughout the past 20 years. The highest concentrations of contaminants remain near population and industrial centers, however improvements in five of six urban bays show sediments in good condition or improving. Notably, pervasive and increasing microplastics were present in Puget Sound sediments.