ANNA MARIA ISLAND — A Red Tide algae bloom that has already been called the worst in a decade spread north over the weekend, reaching this Manatee County community near the mouth of Tampa Bay.

On Monday, clumps of dead fish floated amid the mangroves lining the approach to the Cortez Road bridge to Anna Maria Island, southeast of Egmont Key. Meanwhile at Holmes Beach, another community on Anna Maria, the police appealed via Facebook for volunteers to help them clean up the dead sea life that was washing ashore, offering to provide "masks, gloves and a trash grabber ... to anyone who would like to help."

No one knows for sure when, or if, the bloom will reach Pinellas County's famous beaches. The latest forecast from University of South Florida scientists appears to show the bloom moving north over the next four days — but also shows it being pushed back out to sea by wind and currents.

A blue-green algae bloom that has been plaguing Lake Okeechobee and the rivers on either side of it has made national news and become an issue in the state's political races. But in the meantime, a lingering Red Tide outbreak along about 120 miles of the gulf coast has also been taking a a growing toll on both the state's environment and its tourism economy.

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The Red Tide bloom began back in November, according to Florida Fish and Wildlife Research Institute spokeswoman Michelle Kerr. By hitting the nine-month mark, it's now the longest Red Tide outbreak in a decade, she said. The longest one on record lasted 17 months between 2004 and 2006, she said.

For months it has slowly spread both north and south, each day inching a little further along the coast. Lee, then Charlotte, then Sarasota county beaches were hit hard. Now it's Manatee's turn.

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When Anabelle Filbert saw the murky water and smelled the stench on Anna Maria this week, she lamented her vacation had been wrecked. But she was more concerned that no one seemed able to stop it.

"If this was happening in Chesapeake Bay in Maryland where we're from, it would be a different story," she said. "I feel like they'd be more active."

She's part of a group of 12 friends who for the past dozen years have been vacationing in Englewood, south of Sarasota. This summer, after they heard about Red Tide there, they decided to rent a house in Anna Maria Island.

They paid $5,000 to stay at a house by the beach. Instead of paradise, they found dead sea creatures.

"I almost feel like I should be getting reimbursed for my vacation," said Tracy Frederick, of Philadelphia, who's a part of the group.

Diana White, who has lived in the Fort Myers area for about 20 years, says this is the worst Red Tide bloom she's ever seen.

"It's terrible," she said.

Two weekends ago, White drove up to Anna Maria looking for a beach day free of Red Tide. She convinced a friend to drive up with her again Monday – but as they drove, they discovered the bloom had spread north.

"We saw a sea of green, and then all of a sudden just silver everywhere," said her friend, John Bernhard.

The bloom's toxic properties have so far killed 452 sea turtles, which is about three times the normal amount for this time of year, according to Allen Foley of the Florida Fish and Wildlife Conservation Commission. Most are loggerheads, a threatened species, but some are endangered Kemp's ridleys or green turtles, he said.

And the bloom is suspected of killing 92 manatees so far — 12 in just the past week, according to Martine deWit of the Florida Marine Mammal Pathology Laboratory in St. Petersburg. The numbers can't be verified until the lab can verify the presence of the toxin in the carcasses.

"Numbers may change by the day," deWit said.

More noticeable have been the thousands of fish, including massive Goliath grouper and a whale shark that have washed ashore dead. But Kerr said the fish populations tend to bounce back after a Red Tide bloom hits.

The smell of the fish kills along the Southwest Florida coast has, caused a mini-boom for hotels along the Pinellas beaches.

"I don't have any hard data, but I've heard in my lobby, 'Hey, I used to stay south of you guys but the Red Tide changed my mind this year," said Tony Satterfield, the vice president of operations at Alden Beach Resort in St. Pete Beach. "We have our fingers crossed that thing will not move north."

Tim Bogott, the CEO of TradeWinds Islands Resort, also in St. Pete Beach, said he's picked up a little business from tourists avoiding the stench.

"I hope that it stays away," Boggott said. "We got this several times in the early 2000s and it was pretty devastating."

No one knows what sparks a Red Tide bloom. Small, scattered colonies of the microscopic algae Karenia brevis – named for retired biologist Karen Steidinger, who spent decades studying its properties at the state's marine science lab – live in the Gulf of Mexico all year long. Usually their numbers are so tiny that no one notices.

But every now and then, usually in the late summer or fall, the algae population 10 to 40 miles offshore explodes into something called a bloom. The algae multiply rapidly and spread across the water's surface, staining it a rusty color that gives the phenomenon its name. Then winds and currents carry it toward shore.

Those blooms can last for months, fueled sometimes by nitrate pollution flowing from overfertilized yards, leaky septic tanks and other sources.

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Red Tide is not a new problem for Florida's gulf coast communities. Spanish explorers recorded seeing the blooms from time to time in the 1500s.

The big blooms release toxins that can be deadly to marine creatures. A bloom along the Southwest Florida coast in 2013 killed 200 manatees.

A bloom near shore can also cause problems for humans who inhale the toxins, causing coughing and throat irritation. People who already have respiratory problems such as asthma should stay away from any beach where Red Tide has been spotted.

Some people who have accidentally gone swimming in a Red Tide bloom have reported skin and eye irritation as well as rashes.

Red Tide is no stranger to Tampa Bay. Three years ago, a Red Tide algae bloom that had plagued Charlotte and Sarasota counties for months moved north into Tampa Bay. Soon fish kills began littering the waters and beaches around Pass-a-Grille, Boca Ciega Bay, the Sunshine Skyway and Terra Ceia Bay, and residents of those areas began reporting respiratory problems such as coughing and scratchy throats.

The year before that, in 2014, a bloom offshore deposited dead fish on Honeymoon Island, Madeira Beach and Clearwater Beach.

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Times staff writer Sara DiNitale contributed to this report. Contact Jimena Tavel at jtavel@tampabay.com. Follow @taveljimena. Contact Craig Pittman at craig@tampabay.com. Follow @craigtimes