HEALTH

Lake Okeechobee blue-green algal blooms still toxic with microcystin

Tyler Treadway
Treasure Coast Newspapers

It's proving hard to tell exactly how widespread and how toxic algae blooms on Lake Okeechobee are, despite efforts from space and on the water.

Based on a National Oceanic and Atmospheric Administration satellite image taken Thursday, blooms covered about 110 square miles of the 730-square-mile lake, mostly along the west, northwest and northern shorelines.

But two blooms in the southeast part of the lake were reported Wednesday; and they're toxic, according to data posted early Monday on the Florida Department of Environmental Protection's algae website.

DEP algae website

The ongoing bloom on the lake side of the Port Mayaca Dam also contained the toxin microcystin, but at a level the DEP considers enough to detect, but not enough to accurately quantify.

No algae was found when the site at the dame was checked again late Monday morning, but a sample was taken anyway.

More: Lake Okeechobee bloom at Port Mayaca 3 times to toxic to touch

The hottest bloom, in the southeast part of the lake about midway between Pahokee and Clewiston, had a toxicity level of 19 parts per billion. The federal Environmental Protection Agency says toxicity about 8 parts per billion is toxic in recreational contact.

Another sample taken just to the east of that bloom contained microcystin at a level of 2.1 parts per billion. That's twice the level the World Health Organization says is too toxic to drink.

"Low density" blue-green algae was reported July 10, 2019, on the Lake Okeechobee side of the Port Mayaca Lock and Dam by a crew from the South Florida Water Management District.

At both sites, a crew from the South Florida Water Management District described the algae as "streaky on the surface" with no defined boundaries.

Clouds covered much of the lake's southeast corner when the image was taken, so the blooms reported in that area Wednesday could have been obscured in the satellite image, Sachi Mishra, a satellite oceanographer with the National Oceanic and Atmospheric Administration, said in an email.

"It is highly likely that bloom was there but was well-mixed in the water column due to windy conditions," Mishra said. "In that kind of situation, the satellite can't see all the bloom present there."

The water district typically looks for algae blooms on the lake over two consecutive days: north on one day and south on the other, said spokesman Randy Smith.

Collectors didn't find blue-green algae on the north trip last week, "but did on the south trip, although not where we expected," Smith said.

Also, the NOAA image shows a low-intensity bloom in the north, he added, not enough to see a surface accumulation.

Satellite image of Lake Okeechobee algae bloom taken July 11, 2019.

'Bloom here and there'

The good news: The lake bloom isn't expected to reach the massive size it did in 2016 and 2018, and the Lake O discharges to the St. Lucie River that came in those years aren't likely — at least for now.

"Blooms are popping up here and there," said Paul Gray, a Florida Audubon scientist who's studied Lake O for 30 years. "But with no big pulses of water coming in, the lake isn't highly fertilized, so the blooms are staying relatively small compared to some recent years."

For example:

In both cases, discharges brought the toxic algae to the St. Lucie and Caloosahatchee rivers.

"The blooms we've got now, although they're not huge, are bigger than I expected given the conditions this year," Gray said. "My best bet is that we won't have massive blooms in the lake this year. Of course, algae can do what they want. So we'll have to see how my guess pans out."

More: Algae bloom covers 90 percent of Lake O 

At about 11 feet, 6 inches Monday morning, Lake O remains more than 2 feet lower than its average for July 15 and about 3 feet lower than it was on this date last year.

More: How low should Lake O go to prevent algae blooms?

A "streaky" blue-green algae bloom was reported July 10, 2019, in Lake Okeechobee between Pahokee and Clewiston by the South Florida Water Management District.

But that can change quickly.

If a storm like Hurricane Barry, which dropped more than 20 inches of rain on parts of Louisiana and Mississippi over the weekend, pushed across Lake O and its watershed to the north, the lake could rise dramatically.

More: Lake O discharges begin in advance of Hurricane Irma

That's what happened in September 2017, when Hurricane Irma raised Lake O's elevation more than 3 feet, from about 13 feet, 8 inches to more than 17 feet, in a couple of weeks.

The result: 134 billion gallons of lake water was sent east, the 12th largest recorded discharge ever to the St. Lucie River.