Hood Canal 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
Eutrophication Humankind has increased the rate of phosphorus cycling on Earth by four times, mainly due to agricultural fertilizer production and application. Between 1950 and 1995, an estimated 600,000,000 tonnes of phosphorus was applied to Earth's surface, primarily on croplands. Policy changes to control point sources of phosphorus have resulted in rapid control of eutrophication. Although eutrophication is commonly caused by human activities, it can also be a natural process, particularly in lakes. Eutrophy occurs in many lakes in temperate grasslands, for instance. Paleolimnologists now recognise that climate change, geology, and other external influences are critical in regulating the natural productivity