An unusally lethal, widespread and long-lasting red tide has been identified from northern Pinellas to northern Lee County on the Florida coast.

Diver Mike Miller struggles to convey the horror he has seen on the ocean floor. He struggles because there are only so many ways you can say dead. “I’m talking zero things are alive out there,” Miller said. “The only way to describe it is a nuclear bomb.” Miller and other alarmed divers say they have documented a dead zone 20 miles offshore in the Gulf waters from Johns Pass to Clearwater. ..

“Normally when we get a red tide, you can go a little north or a little west or south or someplace else and dive,” said Ben Dautermen, who takes divers out of Clearwater on his charter boat. “Usually it doesn’t kill every single thing.”

Red tide, an algae toxic to fish and an irritant to humans who breathe its choking vapors, has hung stubbornly to Florida’s west coast for close to three months. Miller and other longtime locals who make their living in the Gulf say it’s the worst outbreak in their experience.

Though it’s not certain that red tide killed the turtles, scientists at the Fish & Wildlife Research Institute in St. Petersburg think the toxic algae wiped out sea life, creating the dead zone Miller and other divers discovered.

The scientists’ theory goes like this: Red tide cells don’t like to pass through water temperature differences of more than 2 degrees. Scientists think a thermocline, or zone of cold water, formed above the warmer water at the bottom, holding the algae bloom there longer than it naturally would stay.

“So the things that would not normally be affected were exposed for longer periods,” said Jeremy Lake, spokesman for the institute.

Harmful algal bloom forecasting and mapping for Florida

A similar red tide has decimated the New England shellfish industry this year.