Lake Apopka and some parts of the St. Johns River have had blooms, although not this many.
And that means if people don’t see it, they’ll swim in it, and the quantity of algae matters.
“The chance of you getting enough of the toxin to impact you would be extremely magnified if there was a high density of algae,” said Bill Kurth with Lake Masters Aquatic Weed Control.
>> Headed to the Gulf Coast? Check for beach advisories about dangerous bacteria first
There are only a few types of blue-green algae known to produce toxins, and there's no way to determine visually if a bloom is harmful, experts said.
The bloom is believed to have come from Lake Okeechobee, and right now, there's no link to Central Florida waterways.
"The blue-green algae came from Lake Okeechobee and flows to the coast. It's not like it's growing on the beaches,” Kurth said.
Most of the residential lakes in Florida are treated to prevent algae.
Health officials say activities on shorelines are safe, but people should not eat fish from affected waters.