TAMPA BAY — About 11 miles separate the area around Port Manatee, where an estimated 215 million gallons of wastewater were recently released into Tampa Bay, and the spot off Manatee County where water samples this week turned up a dreaded result:
In that stretch rests plenty of uncertainty — and worry.
A harmful, toxic algal bloom has been among the biggest fears for scientists, charter captains and lovers of the estuary after polluted water was pumped off the old Piney Point fertilizer plant grounds.
Brian Rosegger, who farms oysters a few miles from the port, said he has “tried to toe the line of being an optimistic pessimist” ever since. That became harder, he said, when he saw that the state identified a low concentration of the organism behind Red Tide near Anna Maria Island off Bradenton.
“Piney Point loaded the gun, and then that first Red Tide positive count, they slammed the hammer back on the gun,” said Rosegger, co-founder of Lost Coast Oyster Company.
Red Tide has recently loomed off counties south of Tampa Bay, and its presence is “not thought to be a direct result of the Piney Point discharges,” according to the Florida Department of Environmental Protection. But nitrogen in the Piney Point wastewater, which a forecast model shows could linger in the shallows around the port, threatens to provide fuel.
“Elevated nutrients have the potential to exacerbate these algal blooms, and increased sampling is ongoing,” the Department of Environmental Protection said in a statement.
A low concentration of the organism in Red Tide can prompt breathing trouble for people along the shore, potential fish kills and shellfish harvesting closures, according to the Florida Fish and Wildlife Conservation Commission. The agency has reported three other samples in lower Tampa Bay with very low concentrations.
Those results are “in the vicinity” of where scientists think the Piney Point discharge is affecting the bay, said Ed Sherwood, executive director of the Tampa Bay Estuary Program. The worry, he said, is that Red Tide and the pollution will drift together as tides, currents and winds move around water.
No fish kills had been reported in Tampa Bay as of Friday afternoon, according to the state. Other samples, including some pulled closer to Port Manatee this week, have not carried troubling levels of Red Tide.
The wastewater from Piney Point, Sherwood said, is estimated to have in a couple of weeks put as much nitrogen into a section of lower Tampa Bay as the area would typically see in a year. He said the nutrient load is thought to be akin to dumping about 100,000 bags of fertilizer into the bay.
Satellite imagery and monitoring from days after the discharge detected a potential bloom of non-harmful algae around the port, Sherwood said. But more recent pictures have indicated that may be dissipating, he said. Sherwood could not say definitively without newer monitoring data.
Peter Clark, founder and president of the restoration group Tampa Bay Watch, scanned the area around Port Manatee on a skiff Friday morning, focusing on Bishop Harbor, a shallow spot in an aquatic preserve just south of where the discharge hit the bay.
A handful of small fishing boats puttered off the port, the water shimmering in the late-morning sun. Sandy bars and dark patches of seagrass colored the bottom.
Clark noted bigger algae covering some of the seagrass. Such growth is typical in the bay and cannot be tied directly to Piney Point. Macroalgae, though, can bury or shade beds if added nutrients fuel a big bloom. Seagrasses are a key building block for the bay, forming a vibrant habitat for fish and other marine life.
“Most everything we see occurs in Tampa Bay, but when you start giving it extra food, it starts growing exponentially,” Clark said. “You don’t want to see (macroalgae) exploding.”
The Piney Point discharge came after owners of the property detected a leak in a large wastewater reservoir, which caused concern that the entire polluted pond could burst, flooding local neighborhoods. The Department of Environmental Protection allowed discharges through Port Manatee, saying it wanted to avoid a catastrophic collapse at the site.
A persistent toxic Red Tide bloom crushed parts of the state’s Gulf Coast in 2017 and 2018, killing fish that washed ashore by the ton and blanketed local beaches.
Scientists say they will have to track the effects of Piney Point on the bay for months at least. It takes time for the environment to respond to excess nutrients. “We’re still at the very beginning of the Piney Point spill in Tampa Bay,” Clark said.