The water in the Indian River Lagoon just south of the Ernest Lyons Bridge and Stuart Causeway in Martin County should be clear, with a sandy or seagrass-covered bottom.

But recently, as he’s been collecting water samples for the Florida Oceanographic Society, Jason Bultman has found the bottom of the lagoon blanketed with brownish-green seaweed, as well as clumps of the stuff, stringy like wet wool, floating on top of the water.

“Some may have been there in previous years,” said Bultman, a resident of Sewall’s Point in Martin County and vice president of the VoteWater Board of Directors. “But it definitely wasn’t like this last year at this time.”

Bultman, and anyone else who’s been spending time on the lagoon, has been looking at blooms of lyngbya.

And as bad as the blooms might be now, they could get a lot worse as the summer progresses.

What is lyngbya?

Lyngbya (pronounced “LING-bee-yah”) is a type of cyanobacteria — like blue-green algae — that grows in tropical and sub-tropical waters, including the Indian River Lagoon.

Indeed, problems with lyngbya have been reported across Florida, on the west coast (Bradenton, Sarasota Bay, Gulfport) as well as the Atlantic coast.

Whereas blue-green algae grows on the water’s surface, lyngbya grows on the bottom, although clumps of the brownish-green stuff often breaks off and floats to the surface.

Cyanobacteria are some of the world’s oldest living organisms, and lyngbya occurs naturally in the lagoon. But it can cause serious problems when it blooms out of control.

Lyngbya produce “secondary metabolites” that can act as feeding deterrents to fish, crabs and other predators. Lyngbya growing on the lagoon bed can overgrow and smother seagrass beds — vital habitat for manatees, fish and sea turtles.

When it floats on the surface, it can kill seagrass by blocking the light the plants need for

photosynthesis.

Lyngbya can contain lyngbyatoxin, which — although not as nasty as the microcystin toxin produced by blue-green algae — at high concentrations can cause skin rash and redness (often called “swimmer’s itch”) and respiratory problems.

But, full disclosure: Lyngbya isn’t even lyngbya — at least, not anymore.

Much like the term “blue-green algae” is a misnomer (the stuff isn’t really algae but a cyanobacteria called microcystis.), the term “lyngbya” has recently been reclassified as Dapis pleousa.

(Read all about it in a June 2018 study by scientists from Florida International University and the Smithsonian Marine Station in Fort Pierce titled “Uncovering cryptic diversity of Lyngbya: the new tropical marine cyanobacterial genus Dapis.”

Here’s a sneak peek:

“In this study, the new genus Dapis was erected from the genus Lyngbya, based on a combined molecular, chemical, and morphological approach. Herein, two new species of cyanobacteria are described: D. pleousa and D. pnigousa. Our analyses found these species to be widely distributed and abundant in tropical and subtropical marine habitats.”

Cyanobacteria like lyngbya (We’re going to keep calling it that; old habits die hard) have been around so long, said Elizabeth Kelly, an environmental scientist with Martin County Public Works, “because it always finds a way to survive in various conditions.”

Where and why it’s growing

So far this year, lyngbya in the lagoon has been surviving, Kelly said, but not really thriving.

“It’s pretty spread out all over the southern lagoon,” Kelly said, “mostly in bays and nooks and crannies where the water is still and shallow — where seagrass also likes to grow.”

What’s feeding the lyngbya this year?

“We don’t really know,” Kelly said. “It’s probably a combination of sources. Lyngbya doesn’t care where it gets its nutrients.”

One source is probably what’s called “legacy” nutrients – nitrogen and phosphorus deposits trapped in the muck at the bottom of the river and lagoon that escape when the muck is stirred up by wind. Nutrients from leaky septic systems “may also be a component,” Kelly said.

What’s not feeding lyngbya this year? Lake Okeechobee discharges.

Whenever the St. Lucie River and lagoon suffer blue-green algae blooms, the cause is always massive discharges of nutrient-rich water from Lake Okeechobee. The most recent round of Lake Okeechobee discharges lasted for 112 days, from Dec. 7, 2024, to March 29, 2025, and totaled 84 billion gallons of water.

But those discharges came at a time when “the water temperature wasn’t high enough” for a serious lyngbya bloom, Kelly said.

That could change in the coming months, even weeks. The perfect conditions for lyngbya to survive – and thrive – are starting to come together on the Indian River Lagoon. And that’s the problem.

Worst yet to come?

First off, lyngbya needs plenty of sunlight. Long summer days are taking care of that.

Like blue-green algae, lyngbya is a bacteria that combine nutrients and sunlight to photosynthesize its food like plants do. Lyngbya thrives in warm water. It looks like summer will be taking care of that, too.

According to data from the Florida Oceanographic Water Ecosystem Surveys, the program Bultman volunteers with to assess trends and changes in water quality throughout the St. Lucie Estuary and southern Indian River Lagoon, temperatures in those water bodies are in the mid- to upper 80s.

“That’s kind of at the lower end of (lyngbya’s) preferred range,” Kelly said. “But temperatures are on their way up. … We’re just now at the beginning of the warmest months of summer, and the wet season is still ahead.”

Officially, South Florida’s rainy season began May 21, when the typical pattern of afternoon thunderstorms began.

“The pattern has begun,” Kelly said. “But we haven’t had any really big rain storms yet.”

The first big storm could provide lyngbya with its final need: lots of nutrients in the form of nitrogen and phosphorus.

That first big storm of the rainy season could trigger what’s known as the “first flush,” when all the nutrients from agriculture and lawn fertilizers are flushed off the surface of the ground and into ditches, creeks, streams and, eventually, the lagoon – giving lyngbya the plentiful nitrogen and phosphorus it needs to bloom big.

After that, the more rain that falls, the more nutrients are washed into the water and the more lyngbya blooms grow.

Solution is prevention

So, how do we get rid of excess lyngbya?

Mechanically removing lyngbya from the water has been tried, Kelly said, but the process damages seagrass beds.

The answer to controlling lyngbya, Kelly said, is preventing the blooms. Since we can’t control the weather (despite what some conspiracy theorists think), we’re left with controlling the amount of nutrients entering our waterways.

“That includes not using fertilizer during months when it’s banned,” Kelly said. “It also includes things like picking up after your dog, not leaving trash lying around, not putting (nutrient sources) down stormwater rains and not cutting your grass so that clippings get in the water. All of those things add nutrients that can feed blooms in the water.”

In the meantime, Kelly said, “We’ve got to keep an eye on the weather, especially for heavy rains, tropical storms and hurricanes.”