Red tide in Sarasota and Manatee remains patchy. Could a new bloom be on the way?

As stubborn and patchy red tide lingers off Sarasota and Manatee counties, experts are keeping a close eye on changes in ocean currents for signs of a new bloom that could make matters worse.

The amount of red tide measured in local waters changed this week, with conditions intensifying to medium levels along most of Anna Maria Island and dropping slightly to low to medium levels in Sarasota County. Medium levels are enough to be considered a bloom. The only location with high levels of red tide measured on Thursday was near New Pass in Sarasota Bay. 

With fall just around the corner, University of South Florida physical oceanography professor Bob Weisberg said the upcoming months could be an important turning point for local red tide. 

Weisberg creates models to track and forecast ocean currents, much like meteorologists track the wind. 

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Scientists first measured red tide in Sarasota County in April and in Manatee County in May, and blooms have plagued the region since. During the summer, hundreds of tons of dead fish washed ashore across Sarasota, Manatee and Tampa Bay.

Red tide became less concentrated in mid-September, and although levels have steadily increased since then, the bloom has become more patchy.

Beach conditions have been mixed in recent weeks, and many visitors have been able to experience crystal clear water, while others have been greeted by more noticeable patches of murky red tide. 

Lessons learned during 2018's red tide event give Weisberg reason to remain leery. 

That year, a lingering bloom from the year before never fully went away, and then Gulf conditions pushed a new red tide ashore to add more strength. The fish kills led to a significant economic impact in Sarasota and Manatee after devastating tourism.

“I wouldn't be surprised to see that happen again this year,” Weisberg said. “Generally, red tide forms in the middle of the continental shelf in late spring through the summer months. Then when the fall sets in, that water – with its red tide that had been offshore – gets carried to the beach and gets concentrated.”

Experts have tracked the ongoing red tide since last winter when it bloomed in Gulf waters near Charlotte Harbor. Cells of Karenia Brevis, the organism that causes red tide, slowly made their way north, leading to blooms in areas where conditions were ripe, Weisberg said.

“This year, it's behaving a little differently,” Weisberg said. “Now that it is fall, and conditions were likely conducive for red tide organisms to grow offshore, and the winds are finally starting to reverse, those new red tide cells could be coming in.”

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Red tide has continued to migrate north along the Florida Gulf Coast carrying cells as far as the Florida Panhandle, where Panama City is dealing with an intense bloom of its own.

“I think concentrations are going to vary over the next month or so, and we will eventually see if we get another red tide bloom or if we just get this patchy-ness coming and going,” Weisberg said.