Florida bills itself as the fishing capital of the world, but from Sarasota north past Tampa Bay and miles into the Gulf, the only fish are dead ones decomposing on the surface.

Boating from Longboat Key to Tampa Bay, out into the Gulf and back to his slip, Wayne Genthner's fish finding sonar picks up only a few bait fish on the Gulf side of Anna Maria Island, close to the beach.

On top of a tenacious red tide that has caused fish kills for months, a 2,000-square-mile low-oxygen zone has smothered bottom sea life upon which fish depend. This dead zone, worse than a similar event that wiped out more than 500 square miles of Gulf bottom in 1971, has people worried, especially those who make their living from the sea.

Since he discovered dead sea-floor in his best fishing spots, Genthner, a charter boat captain, has seen his income drop from $3,000 weekly to $300.

His boat isn't big enough to reach healthy waters, in some cases 30 or more miles out, and he's concerned that the event could drive him out of the business he's been in for almost 25 years.

As far north as Tarpon Springs, charter boat captains report that only a few boats are going out and catching fish. Many are staying in port, saving gas money and doing maintenance on their vessels.

"It's been very, very, very slow," said Don Baize, owner of All About Fishing bait shop in Sarasota. "The only people fishing are ones who haven't been out in a while."

Genthner has asked Gov. Jeb Bush to declare the coast a disaster area and open the door for financial assistance for the marine industry.

Bush aides say he's looking into it.

"It's a unique situation," said Bush spokesman Russell Schweiss. " ... We're reviewing the situation to see what kind of assistance might be available."

Officials from the Florida Wildlife Research Institute and Mote Marine Laboratory say the dead zone is likely tied to the recent and persistent red tide bloom.

The red tide organism exists in the Gulf in small quantities all the time, but when the alga blooms, the neurotoxin it produces kills sea life.

State officials also say parts of the dead area are beginning to show signs of life. But on a seven-hour boat trip Wednesday from Longboat Key to Tampa Bay and then out into the Gulf of Mexico, it wasn't apparent.

Lingering red tide

These days, Genthner is searching for answers instead of fish.

He took University of Miami marine researcher Larry Brand to collect water samples to see if the treated phosphate water coming from the former Piney Point plant in north Manatee County might be a culprit in the red tide or the hypoxic zone.

Since January 2003, the state has allowed the dumping of approximately 1 million gallons a day into Bishop Harbor.

Results won't be back for days, but Brand came to at least one conclusion.

"We had suspected it and a lot of people had been pointing their fingers at Piney Point, but I didn't see any evidence that a lot of nutrients are coming out of there," he said.

The waters in and near Bishop Harbor, where the dumping takes place, appeared clear on this day's trip, with barrel sponges visible from the boat and a few bait fish nearby.

But the journey overall was dismal.

As Genthner's boat cut through Sarasota Bay north into Anna Maria Sound, it passed rafts of dead fish, horseshoe crabs and sea grass.

A pair of bald eagles that perch on a house near where he keeps his boat have been gone for weeks, Genthner said. "The sheer numbers of birds are not what they used to be."

His boat, Wolfmouth, passed few others. No one was fishing the piers on the north and south side of the Sunshine Skyway Bridge.

Aside from the die-off on the Gulf bottom that destroyed their habitat, many fish are gone because of an unseasonable red tide that has remained at different strengths off Southwest Florida since January.

It has killed fish, record numbers of turtles and almost 50 manatees.

Scientists at the Florida Fish and Wildlife Research Institute plan to monitor the low-oxygen zone and continue seeking the conditions that ignite a red tide bloom.

Some scientists think nutrient pollution from land is a factor in fueling the blooms, once they start.

But Fish and Wildlife officials say that's not the case with this one.

Genthner and other boat captains disagree and worry about a repeat next summer, when water temperatures rise and rainfall runoff is pouring into the Gulf.

Not a unique problem

There are areas around the globe that suffer when too many nutrients from farm fields and urban areas wash into coastal waters.

Those nutrients -- more specifically nitrogen and phosphorus -- feed algae and cause massive blooms of the seagoing plants. When the blooms die, the dead plants sink to the bottom and their decay uses up oxygen there.

Warmer waters carrying nutrients cause hypoxia by trapping cooler, saltier water below the warmer, fresher runoff water.

That sets up a thermocline, a boundary between water layers that keeps them apart and keeps surface oxygen from reaching the bottom.

It has happened each summer in Chesapeake Bay since about the 1950s. The influx of nutrients with rainfall runoff each summer causes low oxygen zones, affecting crabs, oysters and sea grasses.

It has happened each summer at the mouth of the Mississippi River, where the dead zone has grown from about 100 square miles in 1988 to an average size of just less than 5,000 square miles. Its largest incarnation was in 2002, when the Mississippi dead zone smothered bottom sea life in more than 8,500 square miles of the Gulf's most productive waters.

Fish and Wildlife scientists say the same forces were not in play for Florida's "dead zone."

Paul Carlson, a researcher with the agency, said the decay of fish and turtle carcasses is providing the organic matter to strip oxygen from the water.

Bait shop owner Baize has his own ideas about what is causing the dead zone, as do the idle fishermen who would rather be on the water.

Boat captains, bait shop owners and tackle distributors also are also talking about the uncomfortable wait ahead, he said.

"Everybody is basically sweating it out," he said.