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Biscayne Bay Had Another Fish Kill. It's Smaller Than Last Summer, But Could Have The Same Culprit

Sunrise showing a fish kill in Biscayne Bay
Courtesy of Kathryn Mikesell
A fish kill spread across northern Biscayne Bay near Morningside in August 2020. A similar, but smaller, kill happened this past weekend.

So far, 250 dead fish have been confirmed in the Tuttle Basin at the bay's north end, where poor circulation means water gets flushed less often.

For the second summer in a row, dead fish appeared in Biscayne’s Bay Tuttle Basin over the weekend.

Miami-Dade County began receiving reports of a fish kill near the 79th Street Causeway late Sunday night, said county’s Chief Bay Office Irela Bague.

By Monday, dead fish had been sighted from Biscayne Point to just south of the Julia Tuttle Causeway and along the bay’s western shore in Miami Beach, North Bay Village and Normandy Isles. None were reported Tuesday.

The county confirmed about 250 dead fish.

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While far smaller than a widespread August 2020 fish kill, Bague said the dead fish show that the bay remains vulnerable to ongoing pollution during rainy summer months.

“It's kind of our new normal until we get a good handle on finding ways to stop the nutrients from getting into the stormwater and systems that convey water into the bay,” she said. “We live on a sponge and everything we dump into the ground ends up in our water system.”

So far, she said, the dead fish appear to be mostly bottom-dwelling species and do not include the rays, barracuda and snook killed last summer.

Two teams from Miami-Dade County, and another from the state's Biscayne Bay Aquatic Preserve, are collecting water and seagrass samples as well as dead fish. The teams want to compare conditions this year to August 2020, Bague said.

“We want to know what was different from last year,” she added.

A year ago, rafts of dead fish were first spotted near the mouth of the Little River. Within days, dead fish were spotted as far south as Virginia Key. Reports continued to climb for five days.

Among the dead marine life, Miami Waterkeeper documented 56 species, including lobsters and eels based on nearly 500 images the group compiled. They estimated about 27,000 fish died. A Waterkeeper report signed by researchers from the University of Miami, Florida International University and more than 40 other groups concluded that low oxygen in bay water — worsened by ongoing pollution — triggered the kill.

Following the report, the county came up with a fish kill response plan to remove dead fish that can worsen conditions.

Scientists monitoring the bay first detected signs of trouble when oxygen levels fell last week, said Miami Waterkeeper executive director Rachel Silverstein.

Given recent heavy rain and high temperatures, Bague said it’s possible low oxygen and pollution again played a factor.

“It's a combination of factors that we're seeing now every summer. Sadly, high heat, quite historic levels, combined with heavy rain events,” she said. “We've had consistent rain since Thursday or Friday of last week, moving all that water through stormwater systems and the canals and everything that comes with it.”

In response to questions from WLRN, Miami-Dade officials said they will be analyzing dissolved oxygen, temperature, salinity along with chlorophyll. They will also look for bacteria typically found in stormwater and septic water as well as the water’s turbidity. A county biologist will also be inspecting the shoreline where fish were found.

In recent months, the county has taken some steps to reduce the pollution, like passing a rainy season fertilizer ban in April. A county task force convened in 2019 also called for tighter pollution limits.

But the more costly and complicated work will be tackling the aging stormwater system and septic tanks increasingly threatened by sea rise and a climbing groundwater table. The county hopes to connect about 100,000 septic tanks to sewer lines, beginning with the most vulnerable, low-lying septics.

Money to begin work is included in next year’s proposed budget, which will undergo its first public hearing before the county commission on Tuesday, Sept. 14.

The county also launched a web site to collect reports on fish kills and pollution to better monitor conditions.

Reports can be filed here, emailed to baywatch@miamidade.gov or called in at 305-372-6955.

You can read more stories like this one by signing up for our environment text letter. Just text “enviro news” to 786-677-0767 and we’ll send you a roundup of stories like this — and more — every Wednesday.

Jenny Staletovich is WLRN's Environment Editor. She has been a journalist working in Florida for nearly 20 years. Contact Jenny at jstaletovich@wlrnnews.org
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