19 APRIL 2021 

Millions of gallons of water laced with fertilizer ingredients are being pumped into Florida’s Tampa Bay from a leaking reservoir at an abandoned phosphate plant at Piney Point. As the water spreads into the bay, it carries phosphorus and nitrogen – nutrients that under the right conditions can fuel dangerous algae blooms that can suffocate sea grass beds and kill fish, dolphins and manatees.

It’s the kind of risk no one wants to see, but officials believed the other options were worse.

About 300 homes sit downstream from the 480-million-gallon reservoir, which began leaking in late March 2021. State officials determined that pumping out the water was the only way to prevent the reservoir’s walls from collapsing. They decided the safest location for all that water would be out through Port Manatee and into the bay.

Florida’s coast is dotted with fragile marine sanctuaries and sea grass beds that help nurture the state’s thriving marine and tourism economy. Those near Port Manatee now face a risk of algal blooms over the next few weeks. Once algae blooms get started, little can be done to clean them up.

The phosphate mining industry around Tampa is just one source of nutrients that can fuel dangerous algae blooms, which I study as a marine biologist. The sugarcane industry, cattle ranches, dairy farms and citrus groves all release nutrients that often flow into rivers and eventually into bays and the ocean. Sewage is another problem – Miami and Fort Lauderdale, for example, have old sewage treatment systems with frequent pipe breaks that leak sewage into canals and coastal waters.

All can fuel harmful algal blooms that harm marine life and people. Overall, blooms are getting worse locally and globally.

Red tide in recent years has killed large numbers of Florida’s manatees, a threatened species. David Hinkel/U.S. Fish and Wildlife Service

The problem with algae blooms

Just down the coast from Port Manatee, the next three counties to the south have had algae blooms in recent weeks, including red tide, which produces a neurotoxin that feels like pepper spray if you breathe it in. Karenia brevis, a dinoflagellate, is the organism in red tide and produces the toxin.

This part of Florida’s Gulf Coast is a hot spot for red tide, often fueled by agricultural runoff. A persistent red tide in 2017 and 2018 killed at least 177 manatees and left a trail of dead fish along the coast and into Tampa Bay. If the coastal currents carry today’s red tide father north and into Tampa Bay, the toxic algae could thrive on the nutrients from Piney Point.

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