New fish kill signals inland pollution releases set Biscayne Bay dead zones, experts say

Pollution from inland sources is affecting oxygen levels in Biscayne Bay and causing more frequent fish kills, experts said on Friday.

MIAMI-DADE COUNTY, Fla. – Piero Gardinali, who is obsessed with water quality, has been watching Biscayne Bay for decades and he was alarmed on Friday while gathering data about a new fish kill.

Gardinali, whose interest in water quality started as an analytical chemist during the 80s in Venezuela, said this time the fish kill area in Biscayne Bay is “much more widespread”

Gardinali studied the effects of environmental pollutants on Galveston Bay while working on his doctorate in the late 90s at Texas A&M University. What he observed then remains true.

“What we do back inland ends up in the bay,” said Gardinali, who now leads the Florida International University Institute of Environment’s Freshwater Resources Division.

Experts have been collecting data about the ongoing fish kill since Wednesday in Biscayne Bay.

Rachel Silverstein, whose interest in the health of coral reefs brought her to the University of Miami, shared Gardinali’s alarm. As the executive director of Miami Waterkeeper, Silverstein is committed to doing everything she can to ensure that the water of Biscayne Bay remains “swimmable, drinkable, and fishable” for all.

“This time we’ve had several thousand fish die. We started getting a flood of reports Wednesday morning,” Silverstein said Friday.

There have been reports of dead fish floating in Biscayne Bay’s northern basin from Government Cut to Haulover Inlet. Experts reported Thursday that the discharge areas of canal C-8 off Miami Shores, across from North Beach, and C-7 off Little River, near North Bay Village, were most affected.

“We’re in the middle right now of the worst fish kill that we’ve seen since the 2020 fish kill,” Silverstein said. “In 2020, in August, we had over 27,000 fish and other wildlife die in a matter of five days and then we had really severe algae blooms ... This time Miami-Dade County actually has a cleanup contractor ... because last time we think that really contributed to algae bloom that happened after the fish kill.”

Miami-Dade County hired a contractor to remove dead fish from Biscayne Bay and workers have been doing so since Wednesday.

Gardinali said Friday that the data shows that oxygen levels were even lower now than back in August 2020. The direct cause of the new fish kill is under investigation, but Silverstein and Gardinali said septic tanks, stormwater runoff, sewage leaks, fertilizer, and other pollutants are going to continue to make it hard for Biscayne Bay to be able to support life.

“We really want people to understand that the root cause of these fish kills is coming from pollution and in short Biscayne Bay just has too much pollution,” Silverstein said.

Gardinali said it’s going to take time to fix the problem.

“The bottom line is pollution and the release of water that shouldn’t be released,” Gardinali said.

Silverstein said Biscayne Bay’s seagrass produces oxygen, so when it dies that’s also when the wildlife starts to die.

“It’s this vicious cycle that’s really hard to come back from,” Silverstein said later adding, “We don’t have time to waste on this because the Bay is literally dying and every year that it worsens, it’s harder to pull back.”

Miami-Dade County is asking residents to report sightings of dead fish to the Division of Environmental Resources Management hotline at 305-372-6955, or e-mail

About the Authors:

Ian Margol joined the Local 10 News team in July 2016 as a general assignment reporter. Born in Miami Beach and raised in Broward County, Ian is thrilled to be back home in South Florida.

The Emmy Award-winning journalist joined the Local 10 News team in 2013. She wrote for the Miami Herald for more than 9 years and won a Green Eyeshade Award.