South of Lake Okeechobee, just beyond 400,000 acres of sugar fields, lie the Everglades’ last line of defense against the phosphorus pollution that is slowly smothering the River of Grass.

They’re an odd blend of nature and engineering: 64,000 acres of manmade marshes, carefully flooded by pumps and canals that divide the landscape into an orderly geometry. They’re stuffed with cattails, muckgrass and other aquatic plants that absorb phosphorus from the water, which mostly comes from the fertilizer spread on neighboring farms.

These marshes, called stormwater treatment areas (STAs), are a key piece of Florida’s plan to restore the Everglades, shore up the water supply for millions of South Floridians and prevent toxic algae blooms on the Atlantic and Gulf coasts that have repeatedly fouled the water and air during peak tourist season. This year, the state is legally required to meet water quality standards that limit how much phosphorus should flow out of these marshes.

But the STAs aren’t on track to comply with clean water rules, according to a recent report from the environmental nonprofit Friends of the Everglades, which analyzed state data.

“Despite billions of dollars invested to clean the sugarcane industry’s pollution, court-ordered water-quality goals are not likely to be achieved,” the Friends of the Everglades wrote in a statement.

Flunking water quality standards would delay plans to send more water south from Lake Okeechobee, with consequences that spread beyond the Everglades. If state officials can’t send extra water from the lake to the south, they may be forced to send it down the St. Lucie and Calloosahatchee rivers, where it flows to the coasts and has caused repeated algae blooms that kill fish, make people sick and sink tourism revenue.

“If you spend 10 minutes around [an algae bloom], you would probably come away with a migraine headache…Your clothes would reek of it. When you take a shower at night, it would be coming out of your pores,” said Rep. Brian Mast, a Republican congressman who represents a district east of Lake Okeechobee that includes Jupiter, Stuart and Fort Pierce. “This is a really big deal.” 

Breaking clean water rules could also invite a new round of costly lawsuits from environmental groups.

The Florida Department of Environmental Protection and the South Florida Water Management District (SFWMD) didn’t respond to multiple interview requests or written questions. But, at a May 14 meeting of the SFWMD governing board, executive director Drew Bartlett said his staff would start publishing regular reports on the STAs in June.

A restoration bottleneck

Florida built the STAs and set water quality standards after two landmark lawsuits accused the state of allowing phosphorus pollution to wreak havoc on the federally-protected Everglades.

Everglades ecosystems evolved to thrive with very low levels of phosphorus. Naturally, less than 10 parts per billion flow through the water. When phosphorus washes off fertilized fields and lawns or seeps out of sewage in septic tanks, it knocks these ecosystems off-balance. The sawgrass that makes up the River of Grass gives way to phosphorus-hungry cattails. Periphyton, a critical algae at the base of the food chain, declines, taking food away from fish, insects and all the predators that eat them.

In short, the Everglades begin to break down.

After settling a federal lawsuit in 1992, Florida spent $2 billion to build a system of STAs, reservoirs and canals to catch and filter phosphorus — mostly from farms in the Everglades Agricultural Area, but also from urban areas that drain into Lake Okeechobee and natural sources.

In 2004, the Friends of the Everglades and the Miccosukee filed another lawsuit accusing the state of failing to curb phosphorus pollution. Under a 2012 settlement, Florida agreed to spend another $880 million on STAs and set phosphorus pollution limits.

These “Water Quality Based Effluent Limits” say the average annual phosphorus levels in the water coming out of the STAs must stay at or below 13 parts per billion two out of every five years, and it must never go above 19 parts per billion. The rules kick in during Water Year 2027, which runs from May 2026 to April 2027.

But, of the five STAs, only one has managed to keep phosphorus levels at below 13 parts per billion, according to state data. The other four have repeatedly hit phosphorus concentrations above 19 parts per billion in recent years.

Overworked STAs

During an April 9 public meeting, water management officials said the STAs have underperformed lately because droughts dried out some areas of the marshes and others were closed for maintenance. Recent improvements, including a new basin designed to smooth the flow of water through one of the marshes, should make the STAs more efficient, executive director Drew Barlett said.

“I’m looking forward to this coming season when we’ll have all our infrastructure,” he said, adding, “There’s still a lot to do” to optimize the system.

But scientists doubt water district officials can squeeze much more performance out of the marshes, which are already working near their maximum capacity. Over the past 31 years, the STAs have consistently removed around 80 percent of the phosphorus pollution that comes their way, district data show. Compared to similar water treatment areas around the world, the Everglades STAs “are top of the class,” according to Steve Davis, the chief science officer at the nonprofit Everglades Foundation.

“We haven’t seen more than a few percentage points variation around the long-term efficiency,” said Thomas Van Lent, senior science advisor at the Friends of the Everglades. “Increasing their efficiency is really hard. It’s almost impossible.”

That leaves two options to bring down phosphorus levels: Make the STAs bigger or reduce the amount of pollution they have to clean. Both would require buy-in from the sugar industry, which owns most of the land and produces most of the pollution in the Everglades Agricultural Area.

“It would be easier with sugar’s cooperation, but that hasn’t happened,” said Van Lent.

Sugar industry groups including the Florida Sugarcane Farmers and the Sugar Cane Growers Cooperative of Florida didn’t respond to multiple requests for comment. Neither did U.S. Sugar, the biggest grower in the Everglades Agricultural Area.

More land

Van Lent and Davis said bigger STAs could clean up more pollution — and they’d build in badly needed back-up capacity for all the extra water the state plans to send south from Lake Okeechobee and the newly-built, $4 billion Everglades Agricultural Area Reservoir, which has been touted as the “crown jewel” of Everglades Restoration.

To expand the STAs, state agencies would have to buy land from neighboring farmers.

In 2010, for instance, the South Florida Water Management District paid U.S. Sugar $194 million for 26,800 acres to expand STAs and build a basin. That was just a fraction of the district’s original plan. In 2008, the South Florida Water Management District board authorized a proposal to pay U.S. Sugar $1.34 billion for 180,000 acres — but then the financial crisis blew a hole in the district’s budget, and officials walked back the deal.

Today, the South Florida Water Management District still seems hesitant to pay the prices sugar growers demand for Everglades land.

At the April 9 governing board meeting, district governor Thomas Hurley asked Bartlett if there was any way to squeeze more efficiency out of the existing STAs using new technologies. “Obviously, acquiring land and building is extraordinarily expensive,” Hurley said.

Florida has a voter-approved $1-billion-a-year Land Acquisition Trust Fund designed to buy land for conservation projects, but environmental groups say state legislators have diverted much of the money to other purposes. State courts dismissed a long-running lawsuit in 2024 alleging the state misspent the trust fund money.

Hunting hot spots

The other option is reducing pollution at the source.

In the 1980s, canals in the Everglades Agricultural Area recorded phosphorus levels more than 30 times higher than natural conditions. The 1994 Everglades Forever Act required farmers to cut their pollution at least 25 percent.

Growers, on average, exceeded that goal: Collectively, they’ve cut their pollution intensity by more than half since the 1980s using common sense techniques like slowing the flow of water across their fields, using berms and sumps to trap fertilizer runoff and regularly cleaning fertilizer buildup out of canals and ditches.

But some farms aren’t pulling their weight. A small group of “hot spot” farms continues to dump phosphorus at concentrations up to 269 parts per billion, according to a 2025 study published by Davis and his colleagues at the Everglades Foundation.

“If we have, say, 200 parts per billion coming in, even the highest performing STA is not going to bring that down to compliance,” Davis said.

The paper counted 55 “high-risk” farms that play an outsized role in polluting the Everglades. The Everglades Foundation didn’t name the farm owners.

“Without addressing the [phosphorus] contributions from high-risk farms, the STAs will continue to struggle to meet regulatory standards,” the scientists wrote.

In the meantime, phosphorus pollution continues to flow into the Everglades — at much lower concentrations than it did before the lawsuits, the Everglades Forever Act and the billions of dollars spent to build the STAs, but not enough for the ecosystem to survive in the long run.

“The process of degradation is very much slowed down, but not stopped,” said Van Lent. “It will get you to the same endpoint, just slower.”

Nicolás Rivero is an environmental accountability reporter at The Florida Trib . He can be reached at nicolas.rivero@floridatrib.org.