September 2006 marked the discovery of the largest
dead zone in the history of Hood Canal. The dead zone may have been caused by low
oxygen levels due to
algal blooms. Algal blooms occur in part because of warm weather and the slow turnover of water in the southern end of the canal, causing the build-up of
nutrients from
fertilizers and leaky septic systems. Organic matter, brought in by ocean water and certain trees, could additionally be contributing to the high nitrogen levels in the basin. Excess nutrients and organic matter causes a body of water to lose oxygen, through a process called
eutrophication. In Hood Canal, eutrophication has led to unwanted algae blooms. Nitrogen combined with sunlight triggers algal growth. A lack of sufficient consumers has resulted in a mass overgrowth of algae in the basin. which has merely been influenced (but not controlled) by anthropogenic activity. Natural causes of hypoxia in Hood Canal include the timing of freshwater inflows, water layer
stratification resulting from seasonal changes in surface temperature, and
climate change. In May 2006, divers searching for
invasive species discovered a mat of marine bacteria covering a stretch where all normal sea life was dead. The mat dissipated five months later. Jan Newton, oceanographer at the
University of Washington, said it was important to note that Hood Canal has had very low oxygen for a long time. Similar mats have been found near
Tacoma, Washington;
San Diego, California;
New York City; and
New Orleans, Louisiana. Critically low oxygen levels, due to increased bacterial growth, were observed in the lower portion of Hood Canal during the summer months of 2004 and 2005. A low dissolved oxygen content in Anna's Bay and Lynch Cove is believed to have been responsible for the corresponding decline in spot shrimp catch by Skokomish Nation fishers within the same period of time. In 2010, there was a massive fish kill in the southern part of Hood Canal. Hundreds of fish and thousands of shrimp were found washed up onto the shore. Jan Newton, a local oceanographer, concluded that the water contained less than 1 milliliter per liter of dissolved oxygen and that such a low level is extremely stressful, often lethal, to the marine life in Hood Canal. The effects of Hood Canal's hypoxic conditions are clearly seen by the public through massive fish kills, but it is important to identify other harmful impacts resulting from a lack of oxygen in the basin.
Eelgrass beds, which are nurseries for salmon and crab, have declined more in Hood Canal than any other area of the Puget Sound. Bottom dwelling
rockfish have also seen a decline due to a lack of eelgrass. Other notable cases of hypoxia and its adverse effects on biodiversity include the large-scale hypoxic zone that appears in the
Gulf of Mexico each summer. The Hood Canal Dissolved Oxygen Program (HCDOP), a partnership of 38 organizations, has been formed to combat the problem. This program will work with local, state, federal, and tribal government policy makers to evaluate potential corrective actions that will restore and maintain a level of dissolved oxygen that will reduce stress on marine life. The HCDOP-Integrated Assessment and Modeling study was started in 2005 to quantify marine processes and watershed loadings, assess biota-oxygen interactions, model key processes to measure drivers of oxygen, and to evaluate potential corrective actions. Government agencies, such as Puget Sound Partnership and the
United States Geological Survey, have used HCDOP's publicly available information to conduct their own assessment and modeling studies of Hood Canal. Though difficult to regulate, a majority of proposed solutions have recommended the regulation of harmful, nearby anthropogenic practices. Human development has caused the most significant damage to Hood Canal's ecosystem. The runoff from septic tanks dumps large quantities of nitrogen into the canal following each rainfall. The best way to solve this problem is to work with the community to create state of the art sewage treatment plants or, at the very least, upgrade old and damaged septic systems to prevent leaks. Several of Puget Sound's counties have taken it upon themselves to create detailed on-site sewage codes. Because the Hood Canal region has experienced logging, as have the majority of watersheds around Puget Sound, the surrounding forests have become heavily degraded. This has caused nitrogen-rich
Alder forests to leach excess nutrients into the water. ==Icing over==