Barely a month ago, Republican Rick Scott held a clear lead in the race to become Florida’s next US senator. Now a tidal wave of toxic algae threatens to engulf the campaign of the outgoing state governor, whom critics have dubbed ‘Red Tide Rick’.

Wildlife officials confirmed on Thursday that the same deadly algae bloom that overran Florida’s south-west coastline this summer, killing dolphins, fish, manatees and turtles and devastating the area’s tourism industry, had washed ashore on several Atlantic coast beaches.

The arrival in the busy waters off Miami-Dade, Broward and Palm Beach counties of the Karenia brevis organism that causes red tide marks a significant escalation of a naturally occurring phenomenon that many believe has been worsened by Scott’s environmental policies.

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His detractors, including the incumbent Democratic senator Bill Nelson, have pounced on Scott for years of rolling back environmental protections and slashing funding for Florida’s water management agencies by $700m. They say the devastating scale and spread of this year’s disaster is a direct result of Scott’s lax attitude to polluters.

Nor is red tide the only problem. Outbreaks of blue-green algae are still choking many of Florida’s inland waterways to the south and west of Lake Okeechobee, with abnormally high levels of the toxin microcystin recorded in several areas. Like red tide, the freshwater algae blooms occur naturally but are fuelled by fertilizers and other industrial pollution in water run-off from farming and sugar production activities in the Everglades.

Toxic 'red tide' algae bloom is killing Florida wildlife and menacing tourism Read more

Meanwhile Scott, who once reportedly banned state employees from using the terms ‘climate change’ and ‘global warming’, has seen a two-point polling lead at the beginning of September dissolve into an advantage for Nelson of almost the same margin. Last month he was harangued during a campaign stop by a crowd blaming him for escalating the red tide crisis.

“You see the result,” Nelson said of his rival at a fiery debate in Miami this week. “He has systematically in his eight years as governor disassembled the environmental agencies of this state. He has drained the water management districts of funding. He even abolished the department of community affairs, which was the growth management agency.

“All of this results in more pollution in the water supply, in the lakes, streams and rivers. We’re seeing all the dead fish and wildlife that are on the beaches.”

Scott hit back by accusing Nelson of promising and failing to secure federal money for urgent repairs to the ageing Lake Okeechobee dyke that he said was crucial to protecting Florida’s water supply.

Facebook Twitter Pinterest Rick Scott is accused by his Democratic opponent of systematically disassembling the state’s environmental protections. Photograph: Mark Wallheiser/AP

Miami-Dade officials closed several beaches to the public on Thursday as the Florida fish and wildlife conservation commission (FWC) reported low to moderate levels of the red tide organism at 25 water sampling points in a 100-mile stretch of coastline from Key Biscayne to Hobe Sound.

On Monday the agency began receiving anecdotal reports of beachgoers in Palm Beach and St Lucie counties suffering from respiratory distress, eye and throat irritations. Red tide has been recorded off Florida’s east coast only eight times in 65 years after traveling the current from the Gulf of Mexico, but never before in Miami-Dade or Broward counties.

Clean water for Florida has become an increasingly prominent campaign issue in recent weeks, with Nelson’s supporters accusing Scott of being an “election-year environmentalist”. They question his finding $3m in state funding for red tide mitigation on Thursday, just weeks before the vote, following years of cutbacks that included eliminating hundreds of water quality monitoring stations and a reduction in enforcement actions taken by the department of environmental protection (DEP) from 1,150 when Scott took office in 2011 to little more than 200 last year.

Scott’s spokeswoman, Lauren Schenone, however, insisted he had a proven environmental record. “Under Governor Scott’s leadership, Florida established the most comprehensive nutrient pollution standards in the nation and, last year, the Florida DEP had a near-record high compliance rate, which means businesses and facilities are following the law and preventing environmental harm,” she said in an emailed statement.

But the Democratic state representative Kionne McGhee, whose district fronts Biscayne Bay, said Scott’s tenure in Tallahassee, and Republican control of the state legislature, had made things worse.

“For the past 20 years of controlling Florida’s air, the land and the environment, they’ve reduced the standards by which the DEP operates. The record speaks for itself,” he said.