Red tide is a harmful algal blooms that can sicken or even kill local wildlife. It also causes respiratory issues in humans and other animals. Chad Gillis/The News-Press
A strong patch of red tide that was along Sanibel Island just days ago has spread out in the Gulf of Mexico but in less dense, less deadly concentrations.
Red tide, or Karenia brevis, occurs naturally in waters off Southwest Florida and can kill fish, marine mammals and sea turtles, as well as cause respiratory problems in humans.
The Florida Fish and Wildlife Conservation Commission on Friday released a report that showed low to medium levels along the coasts of Lee and Charlotte counties.
Collier County waters tested clean of toxic levels, according to FWC reports.
"The high numbers were right along the beaches, and now the water there looks a lot clearer," said Rick Bartleson, a water quality scientist at the Sanibel-Captiva Conservation Foundation on Sanibel.
"What was at the beach has moved away and has kind of spread out," Bartleson said.
"The wind had been pretty strong, so that may have taken a patch of red tide that was affecting the beaches. It may have taken it away for a while."
Strong east winds blew much of last week, and those winds seemed to be keeping the red tide offshore and causing it to disperse.
The National Weather Service expects those east winds will remain in place throughout this week.
Red tide is measured in cells per liter, and last week more than 100 million cells per liter were counted along Sanibel beaches. That concentration was dense enough to be seen from space.
Coastal birds, mostly cormorants, have been treated for red tide poisoning at the Center for the Rehabilitation of Wildlife on Sanibel in recent weeks.
Such birds often have been like canaries in coal mines for forecasting: The birds eat fish that have accumulated the toxin, and the birds end up with neurological problems if the poison builds up in them.