Page "Environmental issues in Puget Sound" Paragraph 23

Oxygen levels will fluctuate throughout the year ; this is due to seasonal changes in nutrient availability, solar radiation, and water column stratification ( layers of water of different density, temperature, and salinity ).

Low oxygen conditions are at their worst in the late summer, after several months of limited flushing and maximum plankton production near the surface.

In some years, oxygen becomes sufficiently depleted that animals cannot survive.

These kills may occur either locally or over a wide area.