Red tides, a type of harmful algal bloom, colour the water rusty orange along the coast of British Columbia in Canada.
Filter-feeders, like clams and mussels, accumulate toxins produced by microscopic algae in their bodies. A shellfish farmer in Massachusetts, Peggy Jennings, couldn't harvest shellfish in 2005 because of a red tide.
Notices are posted along the coast where red tides force closures to shellfish fishing, seen in June 2005.
Here, blooms of microscopic algae give a red tint to water along the coast of China in November 2014.
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