When they arrived in Longboat Key this February, Carol Leone and her family were excited for two weeks of relaxation in the salty breeze.

Within days, they started to cough. Soon, Leone’s voice vanished.

“I just kept getting worse day by day,” she said.

By the second week of her stay, the 76-year-old struggled to breathe.

Legions of dead, rotting fish washed up on the beach. Leone saw the carnage as confirmation of a creeping suspicion: Something foul in the Gulf was making her sick.

She went to an urgent care clinic, where a doctor gave her antibiotics, steroids and an inhaler — but no cause for her illness.

Leone was right about the water being dangerous. Red tide, a toxic algae bloom that hampers beachgoers’ breathing, had reached Longboat Key about the same time as her family.

Her experience wasn’t unique. Millions of people in Florida are exposed to dirty water that puts them at elevated risk of health problems — from coughs to cancer, a Tampa Bay Times investigation has found. Some have wound up in emergency rooms and at doctors’ offices, searching for medicine or answers to mystery ailments like hearing loss and fatigue.

About 1 in 10 residents rely on private wells that can pump tainted drinking water, according to a state estimate. The Times found that colorectal cancer rates exceeded the state average every year for nearly two decades in some counties with high numbers of polluted wells. State lawmakers and regulators have allowed unchecked pollution from cities and farms. At the same time, health officials have failed to warn people about the most severe risks of contaminated water.

To better understand the threat, the Times analyzed five different government health and water quality datasets, including thousands of algae monitoring samples and well water surveys. Reporters also conducted an advanced statistical test using medical admissions data.

The results underscored the gravity of the problem in Southwest Florida. Coastal red tide blooms led to residents visiting hospitals with respiratory symptoms about 6,600 more times than would be expected over two decades, according to Times estimates. Doctors say the most vulnerable are those with long-term conditions such as asthma and chronic obstructive pulmonary disease, which can flare around algae.

Pollution fuels blooms. Toxins — including from red tide and blue-green algae — invade airways and trigger headaches, ragged coughs and itchy eyes. Some residents and visitors say they’ve suffered symptoms for months after being exposed.

Leone’s breathing troubles persisted after she returned to her home in New Jersey. Medical records show she saw a pulmonologist. From 1,000 miles away, Leone now regularly checks Florida’s red tide reports before visiting her son, who lives in Tampa.

“If I encounter the same kind of problem over and over again, I’m kind of asking for trouble,” she said.

Neither the Florida Department of Health nor the state Department of Environmental Protection answered questions the Times sent last month about the findings in this story.

Away from the beach, drinking water also poses risks when polluted by runoff. Many residents have been exposed to high levels of nitrates, a contaminant that medical researchers say likely causes cancer under certain conditions.

At least 3,000 private wells in the last four decades have had nitrate concentrations above the level the federal government considers safe in public drinking water, the Times found. Pollution in dozens of wells has been more than triple the federal limit, which regulators set decades ago to protect infants from a lethal disease caused by drinking tainted formula.

“You can kill a baby very quickly,” said Jeanne Briskin, a retired official who led the U.S. Environmental Protection Agency’s first study of the occurrence of nitrates and pesticides in drinking water. “No one’s supposed to be drinking it.”

For adults, the health risks may not show up right away, but consuming water from a well with high levels of chemicals is unsafe for anyone, Briskin said. Studies have suggested that nitrates may be harmful even at lower concentrations. But federal regulators have not updated standards.

Florida officials don’t test for pollution in all private wells, which serve roughly 2.5 million residents, making it impossible to determine how many people have been exposed. The wells aren’t subject to federal law that limits nitrates in public water supplies.

Homeowners are left to monitor and treat problems on their own, even when contamination comes from neighboring properties they don’t control.

More than 80% of the tainted wells identified by the state were within a quarter-mile of farmland, where fertilizer and animal waste are major sources of contamination, according to a Times analysis of well locations and agricultural data. Rural areas also tend to have properties on septic tanks, which are another source of groundwater pollution.

Most of the wells fall in just a few counties, including Polk and Lake, where for nearly two decades colorectal cancer rates have exceeded the state average. Research elsewhere has pointed to links between the disease and high nitrate ingestion.

But a state fact sheet on nitrate pollution focuses on infants and discourages residents from worrying about cancer.

It says: “No proof of a link to cancer from nitrates in drinking water exists.”

That’s misleading and outdated, experts told the Times. Although more research is needed to understand the dangers, persistent exposure to nitrates puts people at risk, they said.

“With the body of evidence that we have at the moment, you can’t just say there’s no proof of a link,” said Jörg Schullehner, a professor in Denmark who has researched the associations between nitrates and cancer.

Residents who depend on well water are often in the dark about the dangers.

A Lithia widow cannot shake the feeling that dirty water contributed to the cancer that killed her son. She only learned her well had an unsafe level of chemicals when the government tested it. In Plant City, a family drank the water for over 30 years before a friend’s polluted well prompted them to examine their own. They found nitrates more than double the federal limit.

Earlier this year, a Times investigation revealed that hundreds of Florida waterways are dangerously polluted. Politicians and regulators haven’t implemented fixes that could curb contamination from agriculture and development — two of the state’s most powerful industries. Instead, they’ve protected the businesses for decades as waterways have kept getting dirtier.

The environmental toll is dire. Thousands of acres of seagrass have disappeared from places hit hard by algae, like Tampa Bay and Charlotte Harbor. Conditions in the Indian River Lagoon deteriorated so dramatically that hundreds of manatees starved.

Such destruction in nature is inseparable from harm to people in a state where life is tightly knitted with the water. Floridians are beach bartenders, charter captains and weekend paddlers. They pay more to live on the coast. Tourists save up to glimpse paradise. Last year, the state celebrated a record 143 million visitors.

But images of pristine waterways don’t always match reality.

Even where the water looks clear, it can harbor invisible threats.

Red tides bloom, hospitals see uptick

You don’t have to touch or even see toxic algae to get sick.

Waves and boats churn up water, releasing toxins. Sea breezes carry the poison into people’s lungs — sometimes blocks from shore.

Many waterways overloaded by pollution have been spoiled by harmful blooms. Among the most common are red tide and blue-green algae, which cause symptoms ranging from runny noses to nausea to shortness of breath.

Researchers have found links between algae toxins and longer-term medical problems. But Florida’s health department doesn’t explicitly spell out the possibility of persistent harm in online guidance. The health agency said in a statement to the Times earlier this year that the short-term effects of algae blooms “are well known, but the long-term health impacts of toxin exposure need further research.” The state is paying for studies on the issue.

Florida’s online guidance explains that blooms can spread neurotoxins and advises that the best way to eliminate immediate symptoms is to get away from the water. The state urges people to avoid eating shellfish from algae-infested areas because oysters, clams and scallops can accumulate toxins. Shellfish poisoning causes vomiting, slurred speech, dizziness and a tingling sensation in the mouth.

Decaying algae blooms may additionally release dangerous and smelly hydrogen sulfide. But the Department of Health says testing has indicated levels in Florida are “very low” and “non-hazardous,” causing only minor respiratory irritation.

That wasn’t the case for Carmen Driscoll, a longtime kayak guide in Matlacha, where mats of algae clogged canals like a foul stew four years ago. Driscoll, 54, paddled out to document it for a local environmental group.

Soon after, she said, her vision blurred, as if she were looking through a kaleidoscope. She felt intense fatigue and started to stutter. A doctor labeled her a victim of harmful algae bloom poisoning, she said.

There have been nearly 400 formal diagnoses of similar toxic algae exposure over the last decade, according to a Times analysis of medical data.

Driscoll’s symptoms lasted for months — forcing her away from Matlacha and, eventually, from Florida.

“My doctor said, ‘You can’t go and breathe that air,’” Driscoll said. She now lives in Michigan.

Along Florida’s Gulf Coast, doctors know they might see more patients in urgent care clinics and emergency rooms during red tides. People who suffer from chronic respiratory issues such as asthma sometimes need steroids and inhalers to manage labored breathing.

“They start feeling chest tightness — they’ll feel actually short of breath,” said Dr. Siddarth Goyal, who works in the emergency room at Orlando Health Bayfront Hospital in St. Petersburg.

During seasons with red tide blooms, people living in Southwest Florida were 6.7% more likely to visit hospitals with respiratory issues, the Times statistical analysis found.

That amounts to hundreds more hospital visits per year on average in a region that is home to millions.

The findings align with years of academic research on the health effects of red tide. Most recently, a study published in October from the University of Florida found a relationship between exposure to the algae and patients seeking treatment for respiratory and digestive problems.

It was more than just a cough

Amid nasty red tides, more people in Florida have sought help from poison control centers, which operate a hotline featured on red tide advisories.

Between 2003 and this spring, the centers recorded nearly 3,000 reports of red tide exposure. Of those, 140 callers described issues requiring medical treatment, usually in an emergency department.

Further inland and on Florida’s East Coast, it’s not often red tide but toxic blue-green algae that plagues the water.

In 2016 and 2018, bad blooms slicked the St. Lucie River, coinciding with surges of patients at the Martin Health System in Stuart. The system’s leader declared the algae a “public health crisis.”

Robert Lord Jr., the former CEO, remembers staffers hanging signs in the emergency room to ask patients whether they’d been exposed to the water. Some had difficulty breathing. Others had nausea and rashes. Back home, Lord’s wife suffered from minor breathing trouble, he said, but didn’t need medical treatment….

“A lot of people say, ‘Oh, it’s not that bad. Don’t worry about it,’” he said. “You don’t know. Could this be one of those things? If you get repeated exposures, how bad are they for you? What do they cause?”

Some research has linked certain blue-green algae to serious, chronic diseases. Experts are investigating possible connections between a toxin in blooms and ALS and Alzheimer’s disease.

While it’s hard to definitively trace any disease to a single cause, the relationship between blue-green algae toxins and neurological disorders could be thought of similarly to smoking and lung cancer, said Paul Alan Cox, executive director of Brain Chemistry Labs.

“You smoke a cigarette once, it isn’t going to give you lung cancer. Maybe you can smoke it for 20 years — it won’t give you lung cancer. But your risk of getting cancer goes up,” said Cox, whose Wyoming-based nonprofit is searching for medical cures. “There’s probably many paths that can lead to ALS, many paths can lead to Alzheimer’s disease — and this is one risk factor. But why have it?”

Researchers with the Roskamp Institute in Sarasota are similarly attempting to determine whether red tide toxins cause long-term harm — including to the brain.

Among the study’s participants is Brenda Sheets, who in 2018 bought a waterfront condo in Clearwater. One of the worst red tides in modern memory seized Southwest Florida the same year.

Sheets, 64, developed a cough that summer. Her eyes started to throb. Her energy was zapped. She suspected mold in her condo, but tests came back clear.

One night, Sheets couldn’t catch her breath. Doctors told her red tide was to blame and advised her to get away from the water.

She left Florida, only to experience more problems after she returned. She felt dizzy. A stabbing pain shot through her ear.

Sheets said she lost hearing on her left side. Eventually, she couldn’t walk.

“My life was gone,” she said.

She had to go to physical therapy three times a week. She spent 30 days in a wheelchair and about three months using a walker. A doctor at the Mayo Clinic noted in medical records that Sheets blamed red tide for her breathing issues and hearing loss. Sheets provided those records to the Times.

No one could pinpoint the cause of her constant dizziness. After Sheets was called to jury duty when sampling showed red tide near Pinellas County, her doctor wrote a note saying that her health issues could worsen during a bloom. The Times reviewed the doctor’s note; she said she was permanently excused from service.

One day, her husband read that the Roskamp Institute was looking for volunteers for a study. Hearing about other people like her felt validating to Sheets — and also heartbreaking.

In 2022, Roskamp published a study that showed some people may be at risk of neurological problems after encountering red tide, including ailments Sheets experienced.

For her part, Sheets has found a drastic remedy: a second home in Indiana.

Now, at the slightest indicator of red tide, she flees.

Thousands of private wells at risk

Below the surface, pollution accumulates, fouling precious groundwater reserves that are critical to Florida’s drinking supply.

An estimated 2.5 million people draw water from private wells that aren’t subject to the same strict regulation as public drinking water systems — including many in rural places susceptible to agricultural pollution from fertilizer and animal waste. In such areas, homes often rely on septic tanks, which are another source of nitrate contamination.

The Florida Department of Agriculture and Consumer Services, which oversees farms, did not answer questions for this story. State officials have known about high nitrate levels in regions with extensive farmland since at least the late 1980s.

Back then, news coverage shows, there was outrage over elevated nitrate concentrations. In Highlands County, a woman recalled her baby turning blue and needing treatment from doctors, who couldn’t tell her the cause. A year later, county workers happened to sample her well. The water had more than double the federal limit for nitrates.

More than 9,200 wells in Florida have shown levels the EPA considers indicative of pollution, the Times found. About a third of those had nitrate concentrations above the healthy limit for public drinking water set by the federal government.

Regulators don’t apply the same standard to private wells, despite potential health risks, leaving owners to identify and manage contamination. The Florida Department of Health recommends that people get their wells checked at least once a year.

Nitrates aren’t visible, and they don’t have a smell or taste. Basic home filters, like pitchers made by companies such as Brita, don’t remove them. Boiling water to cook or clean can make concentrations worse. Costlier reverse osmosis or ion exchange filters are necessary.

It’s unclear if certain people are more susceptible to problems than others based on diet or factors like genetics. Nitrates aren’t only found in water but in vegetables and processed meats, too.

The U.S. standard for drinking water was set decades ago to protect against a relatively rare illness called “blue baby syndrome” that deprives infants of oxygen in their blood.

A host of other health problems have been linked to nitrate exposure, more recent studies show. Colorectal cancer, thyroid disease and certain birth defects have the strongest evidence for a tie, according to a 2018 review. Researchers have also documented a possible association with pediatric cancer.

In Plant City, Bonnie Hopkins’ well sits at the edge of a strawberry farm. Over a wire fence in her backyard, she sees long rows of plants, berries shining scarlet in the afternoon sun. Within a mile of her house, farmers grow melons, peppers and zucchini across dozens of acres.

Hopkins, 78, said she has thyroid disease. Her daughter had thyroid cancer.

Other family members who have not lived at the home have thyroid issues, too, according to Hopkins. But she wonders whether the well was a factor in her daughter’s sickness.

For more than 30 years, she and her family drank water they thought was clean. The tap tasted fine, Hopkins said, and they didn’t know they should test it. No one had warned them, she said.

After her daughter’s friend discovered pollution in a nearby well, though, her family asked government workers to pull a sample from theirs. They found nitrate levels roughly double the federal public drinking water standard, state data shows.

Hopkins said she won’t drink or cook with unfiltered water anymore. “I don’t trust it,” she said.

Nitrates aren’t thought to cause cancer directly. But they may contribute to a process in the body that produces cancer-causing compounds, scientists say.

Some states publish health guidance that lists cancer and other serious illnesses as potential risks of nitrate ingestion. Not Florida.

Of the six counties where Florida has found the most polluted wells, three — Lake, Polk and Hillsborough — had colorectal cancer rates above the state average for 18 straight years, the Times found. Orange had high rates in 16 of those years, and Hardee in 12 of them. Highlands often had rates below the state average.

Florida’s publicly reported cancer data covers 2005 through 2022. Other factors can contribute to colorectal cancer risk, including alcohol consumption, diet and genetics. It’s the third-most-common form of cancer.

Florida’s testing program has remained spotty, long after health officials detected nitrate contamination in rural areas.

A key part of the program happens when the Department of Health surveys wells in places where the Department of Environmental Protection has found contamination. The state has identified hundreds of polluted wells along Lake Wales Ridge in Central Florida. Naturally sandy soil lets fertilizer pass quickly into groundwater. Agriculture has long dominated the area — a cradle for the state’s famed citrus industry.

The program deals with numerous contaminants, not just nitrates. The state tests near industrial sites and dry cleaners, looking for dangerous metals and other chemicals.

Testing for nitrates appears to have declined in recent years. On average, regulators sample about 40% of the wells they once did, a Times analysis of two decades of data found.

When officials find tainted wells, they offer to provide filters to homeowners, connect properties to public water systems or pay for bottled water. Florida has spent millions of dollars on mitigation. In the last year alone, the state devoted $2.7 million to it for all chemicals. The state will provide filters to residents until wells consistently test below levels considered unsafe by federal drinking water standards.

In Lithia, the government found nitrates above the federal limit in 78-year-old Susan Hudson’s well nearly two decades ago, records show. The experience has left her with painful, unanswerable questions about whether a routine as simple as filling a pitcher of ice water for her family may have harmed them.

Her son, who spent years in the home, died after being diagnosed with colon cancer, she said. He was 49. She suspects the well played a part.

“Nobody can convince me that the water in Lithia is safe,” Hudson said.

Her home is tucked down a narrow dirt driveway near farmland. She knows now that her property is one of several with a polluted well.

But for more than 20 years, she and her husband trusted that the water in Lithia, home to a natural spring, was clean.

Times staff photographer Douglas R. Clifford contributed to this report.

For more information on testing your private drinking well, visit floridahealth.gov/environmental-health/private-well-testing/.

About the data

The Tampa Bay Times analyzed multiple state databases that track harmful algae blooms and nitrate levels in private drinking wells.

For the analysis on red tide blooms and hospital data, we consulted six experts to develop our methodology and to vet our results.

We ran a generalized linear mixed model on red tide sampling data from the Florida Fish and Wildlife Research Institute and hospital data provided through an agreement with the Florida Agency for Health Care Administration. The data includes both inpatient and emergency room admissions. It notes patients’ home ZIP codes.

To identify relevant Southwest Florida neighborhoods, we used spatial software to determine the geometric center of each ZIP code in the state. We drew a boundary to include areas roughly between North Pasco and Marco Island, identifying ZIP codes near the Florida coastline. We only included red tide samples taken within 10 kilometers of those ZIP codes, to be consistent with recent research methods. We also filtered our medical admissions data to isolate patients living in these ZIP codes — meaning the analysis does not include tourists who may have visited a hospital on vacation.

We focused on patients admitted with acute gastrointestinal and respiratory diagnoses, because several studies on red tide have found an association between these conditions and algae blooms. To identify the medical diagnosis codes associated with these issues, the Times followed a methodology recently used in a University of Florida study, filtering for codes mentioned in the paper’s supplementary materials. We excluded records where COVID-19 was listed as a diagnosis.

The medical records include the admission year and quarter, but not the exact admission date. We summarized red tide concentrations by quarter, which we refer to as a season. We considered any season where most sampled days had a maximum recorded red tide concentration greater than 10,000 cells per liter — the level associated with “potential respiratory irritation” — to be a period of potential exposure.

After running the model, we estimated that seasons with red tide blooms were associated with a 6.7% increase in respiratory hospital visits. The relationship was statistically significant (p < 0.05).

Then, using an epidemiological approach referenced by the World Health Organization, we calculated the number of total visits over the time period that are attributable to red tide. We estimated that about 6,600 respiratory visits over the two-decade period could be linked to red tide exposure. We did not find a statistically significant relationship between red tide and gastrointestinal visits.

To determine the number of visits related to toxic algae exposure over the last decade, we filtered the medical admissions for International Classification of Diseases Version 10 diagnosis codes T65.82 and Z77.121.

The reporting also uses data obtained from the Florida Department of Health’s Well Surveillance Program. The program, which began in 1984, samples for a variety of pollutants in private drinking water wells. We focused only on nitrates. The wells included in the dataset were likely used for drinking water at the time of sampling, and data prior to 2000 may be incomplete, according to the department. It’s unclear whether, or for how long, people drank from each well before pollution was identified.

We compared well locations to single-year, age-adjusted rates for colorectal cancer reported by the department at the county level.

Contact Zachary T. Sampson at zsampson@tampabay.com or 727-893-8804. On Signal: ZackSampson.02

Contact Shreya Vuttaluru at svuttaluru@tampabay.com. On Signal: shreyavut.55

Contact Bethany Barnes at bbarnes@tampabay.com. On Signal: Betsbarnes.77