Beginning in late November 1946, and continuing at sporadic intervals until July 1947, a flowering of Gymnodinium sp. caused discolored water off the west coast of Florida. Millions of fish were killed along the coastline and this mortality was always directly associated with the presence of Gymnodinium (Gunter, Smith and Williams, 1947). The phenomenon has been popularly called the "Red Tide."
Ketchum, Bostwick H., and Jean Keen. 1948. "Unusual phosphorus concentrations in the Florida "Red Tide" sea water." Journal of Marine Research 7, (1). https://elischolar.library.yale.edu/journal_of_marine_research/645