To the death and destruction caused by the immediate impact of hurricanes, add the secondary impact of harmful algal blooms.

No, hurricanes don’t cause red tide or blue-green algal blooms, but they can fuel them.

As evidence, look at how Hurricane Milton has spurred a red tide bloom on Florida’s West Coast this year and how Hurricane Irma in 2017 fed blue-green algae blooms on the state’s East Coast.

Red tides occur when algae — in particular a species called Karenia brevis — grow out of control and produce harmful toxins that can kill sea life in the water and, when suspended in the air, sicken people and pets.

An eight-day composite of satellite imagery up to Oct. 21, 2024, from the National Oceanic and Atmospheric Administration shows a red tide bloom along Florida’s Gulf Coast near Tampa.

Scientists say the toxic algae was already present before the back-to-back hits from hurricanes Helene and Milton; but the storms fueled its growth by:

• Bringing up deeper water, which has more nutrients, as they passed through the Gulf of Mexico
• Producing a lot of rain onshore, which led to runoff from the land and added more nutrients to the water.

Hurricanes also tend to push offshore blooms onto shore. And it doesn’t help that red tide usually begins in late September or early October, which coincides with the worst of the Atlantic hurricane season. (Sept. 10 is considered the peak.)

Massive red tides have followed hurricanes before. After Hurricane Charley hit in 2004, a red tide bloom began in January 2005 and lasted almost a year. An equally horrific red tide slammed the west coast in the wake of Hurricane Irma in 2017. By the following year red tide was killing untold numbers of fish and other aquatic animals. That event caused the tourism industry to lose $184 million in revenue, according to news reports.

In fall 2022, less than three weeks after Hurricane Ian slammed the state, red tide appeared off the Sarasota coast. By spring 2023, the bloom was raging from Pinellas County south to Collier County, with thousands of dead fish washed ashore and beachgoers reporting breathing problems along the coast.

Unlike red tides, blue-green algae blooms do their out-of-control growth in inland waters rather than offshore. But the causes of the massive blooms are similar: warm water and plenty of nutrients. Heavy rains from hurricanes – and, to be fair, other weather systems, as long as they’re slow and wet — wash nutrients, particularly nitrogen and phosphorus from over-fertilized fields, into waterways, where the algae feasts.

Think back to 2017, when Lake Okeechobee stayed low — and there were no discharges — all winter, spring and summer. Then Hurricane Irma hit in mid-September, the lake jumped 3½ feet — and the resulting discharges lasted until late December.

Combined with local rainfall runoff, the discharges turned miles of Atlantic beaches and Indian RiverLagoon waters the color of coffee.

Worse than the color of the water was what was in it and what was missing from it. The water contained chemicals from the drained cropland and lawns that killed plankton the fish in the

St. Lucie River and lagoon depend on for food. Diluted by all the freshwater, the naturally brackish estuaries lost all their salinity, which killed oysters.

The massive blankets of guacamole-like algae also shaded and killed most of the sea grass in the St. Lucie and lower lagoon. The waterways have yet to recover.

Besides its aforementioned link to red tide on the Gulf Coast, Hurricane Ian spurred algal blooms on the East Coast as well, but in a different way.

With its torrential rains in Brevard County, Ian caused an estimated 357,300 gallons of sewage to overflow through manholes and a 7.2 million-gallon spill from a sewage treatment plant into the Indian River Lagoon.

The influx fueled algae growth, worsening severe blooms that in 2021 led to the record 1,100 manatee deaths from seagrass loss, the species’ primary food. 

To be clear, hurricanes aren’t necessary for blue-green algae blooms to form. The 2013 Atlantic hurricane season, for example, was well below average and didn’t produce any storms that affected Florida’s East Coast; but the year is remembered for “The Lost Summer” because algae blooms kept people out of the St. Lucie River and parts of the Indian River Lagoon.

Florida has always had hurricanes, and harmful algal blooms are no new phenomenon either. But as nutrient pollution in our waters increases in part due to human activity, hurricanes can stir up ever-more trouble than before. In other words, when it comes to HABs, we don’t have a hurricane problem – we have a nutrient problem.

And until and unless that problem is addressed — expect HABs to follow the storms.