Most aquatic life needs dissolved oxygen in order to breathe. Hood Canal has had a history of low dissolved oxygen levels, which have caused periodic fish kills. A record of fish kills date back to the early 1960s. Recent oxygen levels are the lowest in recorded history, prompting increased concerns about the long-term health of the canal.

In June and October of 2003, and again in September of 2006, low-oxygen conditions killed thousands of juvenile perch and left numerous octopuses, sea cucumbers and other marine life suffocating and dying. In winter, oxygen levels generally rebound with an exchange of water from the ocean. The Washington State Department of Ecology monitoring stations in Hood Canal show that hypoxic conditions may persist year-round in the southern portion. Further, the monitoring station in the north (Bangor) shows that hypoxia may be spreading north with conditions of biological stress for up to six months of the year. Click here for more information about low dissolved oxygen in Hood Canal.

The organic materials associated with fecal pollution deplete dissolved oxygen as they break down in the surface water. In addition, nutrients associated with fecal pollution may provide a nutrient source for algae to bloom. When algae die, their decomposition also consumes oxygen from the water.