MIAMI – An algae bloom that has tainted waters adjacent to the main highway leading to the Florida Keys is moving north and threatens to spread into the heart of Biscayne Bay, playground for thousands of South Florida boaters.

It has already reached the bay’s isolated southern reaches. Brian Gwilliams, a marine service owner and part-time guide who specializes in stalking bonefish and permit in what are usually gin-clear shallows, has watched conditions quickly plummet from pristine to putrid.

“One weekend, I was in Midnight Pass (a shallow cut into Card Sound) and it was crystal clear,” he said. “The next weekend, it was pea soup. It’s gotten so bad, I haven’t gone back down there.”

Near Broad Creek one sunny day last week, the tidal flush across Cutter Bank – carpeted with some of the bay’s lushest sea grass – flowed brown as coffee, thick with decaying material. Along the mangrove shore near the Turkey Point nuclear power plant, the calm shallows looked as weirdly green as artificial turf: algae in full and vibrant bloom.

Anglers, environmentalists, scientists and managers at Biscayne and Everglades National parks worry when, where – and if – the bloom of unprecedented persistence will stop or dissipate.

“Nobody knows how long this stuff is going to sit out there,” said Mark Lewis, superintendent of Biscayne National Park. “This is a low-circulation water part of the bay. It will be months and months before this stuff gets washed away.”

Though its size and intensity changes month to month, the bloom has lasted nearly a year and affected more than 175 square miles – from northeastern Florida Bay on up through Barnes and Card sounds and, during the last month, into southern Biscayne Bay.

It’s the worst explosion of algae since blooms devastated swaths of Florida Bay more than a decade ago.

While there is no indication the green algae is toxic to marine life or humans, long-lasting and dense blooms can kill sea grass, sponges and other bottom plants, with ripple effects for the crabs, shrimp and fish that depend on them. And once the stuff does die, the decomposing mass sucks up vast amounts of life-giving oxygen.

“I was hoping with the rains and everything, it would change the situation, go into nutrient limitation and drop off,” said Joe Boyer, associate director of the Southeastern Environmental Research Center at Florida International University, which monitors coastal quality under a contract with the South Florida Water Management District.

“It seems to be just self-perpetuating.”

Scientists know what set off the bloom – an excessive level of nutrients – but they haven’t pinpointed its source.

An analysis completed in July by a water district team pointed to several possible suspects: Three hurricanes in three months last year may have thrown rotting leaves and other organic matter into the bay. Rains also sent storm runoff flowing down the C-111 canal in South Miami-Dade County.

Then there’s the $270 million project to widen the 18-Mile Stretch between Florida City and Key Largo. The bloom was first spotted around the road project, and environmental groups have questioned a key part of the construction called “soil mixing.”

Hundreds of acres of destroyed mangroves were mulched, then mixed with the thick wetland soil they grew in, along with cement and a metal “slag” material to form a stabilizing layer under the roadbed. One group, Audubon of Florida, had called for a halt to construction until the source of the bloom is identified.

The Florida Department of Transportation rejected that request. The agency said the soil mixing has ended and argued that no data clearly implicates the roadwork.

Dean Powell, director of watershed management for the water district, said that a multiagency research team has stepped up monitoring and testing, including taking soil core samples to assess possible impacts from soil mixing.

It may be easier to rule out some suspects than to identify one precise trigger.

“It’s probably multiple factors,” Powell said. “I don’t know if there is much you can do to change how it spreads. What we’d like to do is figure out what caused it, to prevent it from happening again.”

Scientists say nature could cure the problem.

A hurricane or strong tropical storm could stir things up enough to knock the bloom back. So could a cold front, which typically kills algae, but this bloom weathered last winter.

It’s difficult to predict how deep into Biscayne Bay the bloom might move.

Powell said the bloom’s density and size have waxed and waned as the algae front has crept north.

The stronger currents and tidal flows in much of Biscayne Bay could provide a measure of protection, flushing algae from the bay more effectively than in the isolated basins on either side of the 18-Mile Stretch, where the bloom has lingered longest.

But circulation in the bay tends to move north, scientists said. The fear is that the bloom could settle in spots, particularly over sensitive sea grass beds along the mainland coast.

While multiple agencies are monitoring the bloom and it has drawn considerable attention in the Florida Keys, it’s largely been out of sight and out of mind in Miami except to flats anglers like Gwilliams.

That will change fast if more heavily traveled sections of the bay go green, he said.

“It’s not going to be important until it passes Black Point and it gets up into Cocoplum and the Coral Gables Waterway and starts turning the bottoms of Hatterases (a high-end yacht brand) purple.”

(c) 2006, The Miami Herald.

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Distributed by McClatchy-Tribune Information Services.

AP-NY-09-24-06 1930EDT

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