Red Tide is the name applied to a condition in which portions of the ocean become overrun with an algal bloom of phytoplankton. Despite the nickname, not all Red Tide is red. Sometimes an algal bloom can be present in sufficient quantities to make the water and nearby air dangerous even without coloring the water at all. Some Red Tides - increasingly, most of them, in fact - produce natural toxins and depletion of oxygen in the seawater. Scientists say they don't know everything about how and why Red Tide forms when and where it does, but I like the quote from here likening the delicate balance of algae in the ocean to that of the intestinal flora in our own stomachs.
There is no known case of Red Tide dating before 1793, when one occurred in Canada. When you look at the list of significant incidents since then, they're all weighted to modern times: there was a major outbreak in 1840, then 1972, then 2005, 2011, 2012, 2013 and 2014. Are you startin' to see a pattern here, well, huh, are ya?
The Red Tide is back with a vengeance this summer, and though it hasn't yet been definitively linked to the recent fish die-off on Honeymoon Island and Caladesi Island, it's a safe bet for the smart money.
Of even greater concern to me, though, is how the Red Tide may be a canary-in-coalmine indicator of increased hydrogen sulfide and methane in the area.