Red Tide is the common name for algal blooms, which occur when certain algae rapidly accumulate and form dense patches near the water’s surface. When dense enough, these algae color the water: red, most commonly, but sometimes green, purple, and pink, too.
Red Tides in the Gulf of Mexico are caused by the algae Karenia brevis, which—when high enough in concentration—releases a neurotoxin that paralyzes the central nervous systems of fish and renders them unable to breathe.
People experience respiratory difficulty when these neurotoxins are blown into the air and often report severe illness after eating shellfish contaminated by Red Tide toxins. A 1793 Red Tide in Canada caused over 100 human deaths and thousands of reported illnesses.
These photos were taken last October on Gasparilla Island, Florida, a month after a Red Tide in the Gulf of Mexico. This past week, the National Weather Service issued its first health alert about Red Tide.