Algal blooms ‘happen when waste water from farms, factories and dwellings carries large amounts of normally scarce nutrients like nitrogen, potassium and phosphorous into rivers, lakes and seas (see Nitrogen pollution and fertilizer). Algae, often unicellular ones, lap these nutrients up and breed like billy-o. These blooms are occasionally dangerous, if the algae involved are toxic,’ (Source: ‘Strange Brew’, The Economist January 3rd 2015, p.61).
On its long journey south the water [from the Mississippi as it empties into the Gulf of Mexico] has scooped up nutrients such as nitrogen and phosphorus, mainly from the fields of the Midwest. So much so that agriculture’s gift to the gulf is a “dead zone”. The excess nutrients cause algae to bloom, consuming all the available oxygen in the sea, making it hostile to other forms of marine life. Creatures that can swim away, such as shrimp and fish, do so; those that cannot, die. In the four decades since the dead zone was discovered it has grown steadily. Today it covers 6,700 square miles, an area larger than Connecticut,’ (Source: ‘Nutrient pollution, Blooming horrible’, The Economist June 23rd 2012).