The dead fish started showing up on Wednesday, the white shock of their upturned bellies dotting the shoreline near Morningside Park and the Tatum Waterway. They stunk.
By that afternoon, scientists and advocates say it was clear that Biscayne Bay was experiencing another significant fish die-off, likely caused by the same low oxygen and high pollution levels that caused the last major fish kill in August 2020.
“This is the worst fish kill we’ve seen since the 2020 event,” said Rachel Silverstein, Miami’s Waterkeeper. “This should really ring to people as massive alarm bells that this bay is dying. This is what a dying waterway looks like.”
Early testing from Miami-Dade’s Division of Environmental Resources Management, which counted more than a thousand dead fish, said the culprit is the same as last time: low oxygen levels.
Fish start to struggle when oxygen concentrations dip below 5 milligrams per liter, and measurements taken Thursday at the mouths of Little River and Biscayne Canal showed levels near zero.
Residents also reported seeing fish near the surface of the water gasping for air and struggling, along with clumps of dead flounder, toadfish and pufferfish.
By Friday morning, DERM and Waterkeeper said there were fewer reports of dead or dying fish coming. The county hired contractors to scoop up the rotting fish, which mostly collected near Pelican Harbor and in North Bay Village around 79th Street. Miami Beach was also cleaning up fish corpses on the eastern side of the bay.
Why is this happening?
A squad of researchers from county, state and federal environmental agencies, along with academics from the University of Miami and Florida International University, hit the water Thursday to figure out what exactly caused oxygen levels to plummet this time.
Henry Briceno, a research professor on water quality at FIU, said it’s too early for scientists to know what happened, but they noticed that oxygen levels started dropping late last week. Buoys in Little River equipped with devices to measure water quality noticed oxygen levels were dropping but the water was getting saltier, the opposite of how things usually work.
“You see more oxygen when you have saltier water. In this case, we’re seeing saltier water with lower oxygen concentrations. That’s weird,” he said.
Researchers also noticed brown and cloudy water surging out of Little River and the Biscayne Canal, near clusters of dead fish.
Ahead of Hurricane Ian’s arrival a few weeks ago, as well as the recent king tides, the South Florida Water Management District pushed water out of its canals to make room for future rainfall and keep salty high tides at bay. That water could have swept up groundwater pollution, like human waste spilling from leaky septic tanks and sewage pipes, or land pollution, like dog waste, car oil and fertilizer, into the bay.
But Briceno cautioned that it’s still unclear if pollution from Little River, although long known as a stress on the bay, was the trigger for this particular fish kill. That’s because scientists haven’t been able to check if nearby groundwater was equally polluted or had the same change in saltiness and oxygen, a sign that the issue was more widespread.
Another question mark: the 1.2 million-gallon sewage spill in Miami Beach near Indian Creek late last week. The city managed to recover about 220,000 gallons, but more than a million gallons ended up in the bay.
Researchers are also curious if wind levels or water temperature played a role.
Warmer water holds less oxygen, so summer heat can sometimes set off low oxygen levels and fish kills. But unlike the August die-off, Biscayne Bay was a little cooler this week. In fact, Wednesday marked the coldest day of South Florida’s mini cold front with temperatures dipping into the high 60s.
“At the end of the day, I cannot put my finger on the root cause of this issue,” Briceno said. “We need more data.”
Irela Bague, Miami-Dade’s Chief Bay Officer, said scientists will have a better sense of how many fish died, as well as the cause of their death, by next week. It’s already clear, however, that this die-off likely isn’t as bad as the 2020 one, but it may be worse than the “small and disparate” event in August 2021.
“Right now we’re just in recovery mode,” she said. “This seems to be becoming an annual event.”
The root cause: unchecked pollution
Whatever the specific trigger may have been this time, Silverstein said it’s just a symptom of the poor overall health of the bay. For years, unchecked pollution has gushed into Biscayne Bay, shocking the environment with too many nutrients that kill off the seagrass that lines the sand at the bottom.
That seagrass oxygenates the water and provides a safe habitat for fish, and it’s experienced a dramatic die-off in recent years.
“None of these underlying factors would cause a fish kill without the pollution,” she said. “If you want a Biscayne waterway that’s full of life, we have to act urgently to eliminate septic tanks, fix sewage leaks, address stormwater and stop all the fertilizer runoff.”
Miami-Dade is tackling each of those factors, some more intensely than others.
The county is pursuing millions of dollars in grants to convert leaky septic tanks to sewer lines and focusing its efforts on the spots where those leaks are most likely to affect the bay, as well as passing new county-wide laws guiding how septic tanks are approved and maintained. It’s also running a few pilot projects to test new technology to filter stormwater and catch trash before it flows into the bay.
Earlier this year, the county also passed a new law banning residents from using fertilizer on their lawns during the rainy season, when it’s most likely to get washed into the bay.
Bague said the county has begun work on 50 of the 68 recommendations made in the latest Biscayne Bay Task Force Report and wants to see residents step up and do their part as well.
“We’re doing at the high level what we need to do. The public really needs to take note of this,” she said. “Our bay is sick and it gets really sick at certain times of the year.”
Residents can report dead or struggling fish to the DERM hotline at 305-372-6955, email [email protected] or use the 311 Direct app.