Fish kills can start when levels reach 10,000 cells per liter. In 20 Florida locations, concentrations were higher than 100,000. Health alerts for red tide have been issued in Lee, Collier counties.

Anglers rely on NOAA data to set catch limits that sustain both their livelihoods and the region’s fish stocks. A fisherman pulls up to unload his catch as pelicans gathered at the Cortez docks in ...