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.
“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.