Biscayne Bay, famed for its clear water and trophy bonefish, has been tainted by an algae bloom that may rank as the largest ever recorded in the bay.
The bloom, which has left large swathes of the bay looking like pea soup and smelling like a Porta-Potty, appears to pose no human health risks and hasn’t produced any noticeable fish kills — at least not yet. But if it persists too long, it could damage fragile sea grass beds, disrupt the marine food chain and make boating, fishing and sand-bar bikini parties considerably less pleasant.
Bob Branham, a top fishing guide who has spent more than 30 years poling fly-fishing clients across Biscayne Bay’s shallows, said he’s never seen the bay as foul as the patches he crossed inside of Elliott Key last weekend.
“It’s got kind of a greenish tint when you run over it and you get that smell right away,’’ said Branham, who fears a re-run of the disastrous explosions of algae that devastated fishing in Florida Bay in the Florida Keys in the early 1990s.
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“Some of those areas have not recovered yet and probably never will,’’ said Branham. “It’s not a good sign.’’
Scientists share the concerns. Experts from Miami-Dade County, Biscayne National Park, federal and state agencies and the University of Miami and Florida International University ramped up surveys this week, trying to get a handle on how big and bad the bloom is and figure out what triggered it.
With only limited testing so far, they won’t rule anything out yet but it doesn’t appear related to a sewage spill. Despite the rotten odor emanating from churned-up waters, no telltale indicators of human waste have been found.
Researchers also say there’s not enough evidence to pin blame on another obvious suspect: Billions of gallons of storm runoff, carrying farm and yard fertilizer and other nutrient pollution that can feed blooms, have poured into the bay from three major coastal flood-control gates between Cutler Bay and Homestead during the past weeks of heavy rain.
One thing is certain. Miami-Dade County records, based on a bay water quality monitoring program going back at least three decades, show nothing approaching its size and intensity.
“We are seeing very unusual concentrations of algae and distribution in areas where we typically don’t see these events,’’ said Susan Markley, chief of water resources for the county’s regulatory and economic resources department.
Chlorophyll counts, a measure of algae concentration, have ranged up to 50 times higher than normal healthy conditions in some areas. The bloom also has spread across much of the bay. During survey trips earlier this week, researchers from the National Oceanic and Atmospheric Administration found three large and separate patches, some worse than others.
Pushed by winds and tides, blooms often move around and can quickly shrink or swell, but this week the most intense concentrations were in Card Sound south of the Turkey Point nuclear power plant’s sprawling cooling canal network. Another strong patch spread over a chunk of the central bay south of the Rickenbacker Causeway. A weaker bloom was found near the mouths of three major flood-control canals in the southern end of the bay.
Seasonal algae blooms are common in the coastal waters of South Florida, particularly in shallow areas with limited circulation, high salinity and warm waters. Florida Bay suffered massive blooms in the 1990s and has seen sporadic outbreaks since.
Barnes Sound, south of the Card Sound Bridge, has been hammered numerous times over the years — especially when water managers opened the flood gates of the C-111 canal, which drains the farms and nurseries of South Miami-Dade. In 2006, a massive long-lasting bloom crept from Northeast Florida Bay into Barnes Sound and reached the southern reaches of Biscayne Bay — a milky cloud scientists blamed on some combination of hurricanes, polluted farm runoff from the C-111 and a $270 million project to widen the 18-Mile Stretch between Florida City and Key Largo.
But that bloom never moved north of Turkey Point into the open bay, where a strong tidal flush tends to limit algae development and helps maintain water clarity — a selling point fishing guide Branham highlights on his website: “We have no algae problems, no jet skis, and plenty of bonefish, permit and tarpon.”
But this one appears to have staying power, with the first anecdotal reports from county water sampling crews and anglers coming in mid-June.
“When I first heard about it, my initial reaction was that it would probably dissipate quickly,’’ said Chris Kelble, a research oceanographer at NOAA’s Atlantic Oceanographic and Meteorological Laboratory on Virginia Key. “I’m frankly surprised and concerned that it hasn’t happened with this one.’’
It’s the same period when much of South Florida has been drenched by tropical deluges. Since July 1, the southeast coast has received more than double the typical rainfall for the month, according the South Florida Water Management District. Since June, water managers also have lowered Miami-Dade’s canals twice in anticipation of storms and are also releasing water into Miami-Dade’s canal system from swollen Everglades marshes north of Tamiami Trail.
Over the last month, district spokesman Randy Smith said the three major flood gates north of Homestead’s Bayfront Park have been dumping an average of 673,200 gallons a minute into the bay — enough to fill 45 backyard swimming pools. There have been no releases from the C-111 canal further south, he said.
It adds up to a huge shift in water chemistry for the bay — steady daily slugs of fresh but turbid water, carrying all sorts of stuff, from decaying bits of plants to sand, soil and various pollutants, including nitrogen and phosphorus from farm and yard fertilizer.
“We can’t rule out the discharges may be having some sort of impact on the bloom, but we’re still waiting for the scientists to come up with some sort of determination,” said Smith.
That could be difficult, said Markley. Water samples don’t show unusually high nutrient levels, she said, but the blooms may have already absorbed much of it. There are other questions as well. The weakest blooms are around the mouths of the drainage canals and though it’s a high volume of runoff, similar amounts have been released in the past without triggering blooms. The bloom also appears to have started before the recent big rains
“We really don’t know exactly what is different this year,’’ Markley said. Salinity levels, water temperatures and a host of other factors all can play a role in fueling algae explosions.
Unlike red tide and other types of toxic algae, which can paralyze and kill fish, manatees and other sea life and cause respiratory problems for people, these blooms don’t pose a health risk to the public, said Christopher Sinigalliano, an environmental microbiologist at NOAA’s Virginia Key lab.
The blooms are primarily diatoms, which he described as tiny glass-like shells. The normally benign microscopic marine plants are commonly found in bay waters but at much lower concentrations. Why the blooms smell so fetid also isn’t exactly clear, but it could be the smell of all the dense “biomass” decaying, not unlike a pile of rotting yard clippings.
Aside from the odor, the most immediate concern is for the marine environment. Lengthy blooms can block light vital to seagrass and other bottom plants and animals that provide food and shelter for everything from baby lobsters to bonefish. Dense concentrations also can choke sponges, filter-feeders that help keep water clear, with the sticky algae filling their internal canals with a mucous-like ooze.
The encouraging news so far, said Sinigalliano, is “we don’t seem to be seeing a lot of ecological damage.’’
But historically, blooms also can go through troubling transformations, with one variety giving way to other potentially toxic strains.
“It’s not uncommon for blooms to progress and change over time in their composition,’’ said Steve Blair, a senior biologist for Miami-Dade’s environmental agency. “It’s fine now. There doesn’t seem to be any human health concerns, but we have to keep watching it.’’