It was the first outbreak of red tide in the area since 2002, and thousands of fish have already washed ashore.
"I don't know if we are dealing with a couple-of-days scenario or a week-long scenario," said Daniel Salmon, County's director of parks, recreation and ocean rescue.
Salmon said he saw a dead turtle on the beach, as well as large red bass and a stingray he estimated at 100 pounds.
Beach-goers also were experiencing scratchy throats and eyes near the water.
"There is definitely an irritation when you get out of your vehicle," Salmon said.
He said the fish were already dead when they reached shore and had begun to decompose. He said his primary focus now is how to remove two days' worth of carcasses.
Lifeguards in put out double red flags at three parks to warn people to stay out of the water. Later, the county's Health Department issued a health advisory.
"I think the double red flags will fly until we get some notification from the health department that the current issue is over," Salmon said.
Health department spokesman Wade Sparkman said the advisory will be in effect until the tide dissipates.
Lifeguard George Paugh said he and co-workers at the beach were experiencing coughs and irritation Wednesday morning.
"Each one of us is coughing a little bit more," he said.
Red tide makes sporadic appearances in the area, reaching around from the Gulf of Mexico, where it is more prevalent.
Symptoms of respiratory irritation may persist while beach-goers are near the shore, health advisory said. Those with such problems are advised to stay away from the beach areas. The symptoms usually go away once a person leaves the beach area. Those living in beach areas are advised to close windows and run air conditioning.
