National Oceanic and Atmospheric Administration researchers said their model suggests algal blooms forming off Florida’s west coast are supplied with additional nutrients that apparently originate from the Mississippi River in a process driven by normal seasonal wind patterns.

We found the concentration of nutrients needed to start the Florida red tides is much lower than previously suspected, said NOAA oceanographer and lead author of the study Richard Stumpf. The hypothesis means that offshore areas should be examined for both small increases in nutrients and modest concentrations of the algae at the start of the bloom season.

Red tide is the common name for concentrations of phytoplankton that often appear red due to their density, although not all algal blooms are dense enough to cause water discoloration.

NOAA scientists said harmful algal blooms occur in the waters of nearly every U.S. coastal state, with direct economic effects in the United States estimated to average $75 million annually.