Human-caused ‘dead zones’ threaten health of Puget Sound

Kent Reporter

During the summer of 2015, thousands of dead eels washed up on the beaches of the Hood Canal. These eels suffered a familiar fate for marine life in many parts of Puget Sound and its long, shallow offshoots when the level of dissolved oxygen in the water had become too low to support them.

Elsewhere in Puget Sound, large blooms of algae or jellyfish can be seen drifting in the currents, especially during summer months. These floats indicate that there’s too many nutrients in the water. Algae thrive on these nutrients, and when they die and sink to the bottom, the bacteria that decompose them sucks up oxygen, leaving little for eels, fish and other animals.

One of the most common nutrients that boosts these algae blooms is nitrogen, and according to the Washington State Department of Ecology, wastewater treatment plants contribute significantly to low oxygen levels. Nitrogen in urine isn’t treated in most wastewater plants anywhere in Puget Sound, and King County’s West Point plant is one of the largest.

A 2019 report from the Salish Sea Model found that during the warm spring and summer months, wastewater treatment plants account for about 70% of the excess nutrients in Puget Sound. Much of the nitrogen in Puget Sound is from the Pacific Ocean, but human-caused nitrogen compounds this.