By Coral Gables Gazette staff
Dead fish and thick mats of sargassum have turned up in the waters around Gables by the Sea, bringing a familiar late-summer water-quality concern into a Coral Gables neighborhood during an extraordinary year for the floating seaweed.
No cause has yet been established for the fish deaths reported locally. But the combination warrants attention: when large quantities of sargassum become trapped in shallow, warm water and begin to decompose, they can drive down dissolved oxygen to levels that stress or kill fish.
A record year for sargassum
Sargassum volumes across the broader Atlantic-Caribbean system have been exceptionally high this year.
The University of South Florida’s Optical Oceanography Laboratory, which tracks the seaweed by satellite, reported about 5 million metric tons in the Gulf of Mexico in June alone — nearly twice the previous Gulf record. The same sprawling sargassum belt extends across the tropical Atlantic and Caribbean, with currents carrying floating mats through the Florida Straits and toward Southeast Florida.
Researchers have described 2026 as one of the largest sargassum years since the current bloom cycle began in 2011, with substantial beaching expected across the Caribbean and Florida.
The seaweed originates far offshore as part of what is known as the Great Atlantic Sargassum Belt. Winds and currents push it through the Caribbean and Florida Straits, where mats can reach Biscayne Bay and the canals and waterways connected to it, including those around Gables by the Sea.
Why decomposing seaweed matters
Sargassum itself is not inherently harmful.
At sea, floating mats provide habitat and shelter for fish, crabs, sea turtles and other marine life. Problems can develop once large quantities become trapped along shorelines or in shallow, poorly flushed waterways and begin decomposing.
That decomposition consumes dissolved oxygen in the surrounding water. Warm temperatures make the problem more acute because warmer water naturally holds less oxygen. Nutrient pollution, algae, stagnant conditions and stormwater runoff can compound the effect.
The result can be conditions in which fish are unable to obtain enough oxygen to survive.
Biscayne Bay has shown that vulnerability before. A massive August 2020 fish kill was attributed to several factors acting together, including high water and air temperatures, low winds, poor circulation, unusually low tides and nutrient-laden stormwater entering an already stressed portion of the bay.
That history also underscores an important distinction in the current Coral Gables situation: the presence of sargassum alongside dead fish does not by itself prove that the seaweed caused the deaths. Dissolved-oxygen measurements and other water-quality testing are needed to determine what is happening in a particular waterway.
What the city can do
Coral Gables Public Works oversees the city’s waterways and can respond when accumulated seaweed becomes a problem.
Public Works says the city has a boat capable of removing seaweed from local waterways and can deploy it when conditions warrant, including significant buildups associated with fish deaths. Removal is not performed automatically on a routine schedule.
Residents who notice substantial accumulations can contact Public Works at pwdepartment@coralgables.com or 305-460-5000.
What residents should do if they see dead fish
Residents who spot clusters of dead or dying fish should report them directly to Miami-Dade County’s Division of Environmental Resources Management, or DERM, the county’s lead agency for fish-kill and algae-bloom response.
DERM’s environmental complaint line, 305-372-6955, is staffed 24 hours a day. Reports also can be emailed to environmentalcomplaints@miamidade.gov or submitted through the county’s 311 system by phone, app or online.
The county says reports are most useful when they include a specific address or location and, when possible, photographs or video. That information helps investigators distinguish active events from isolated or already-resolved conditions.
A waterfront issue to watch
The conditions at Gables by the Sea are expected to surface publicly Thursday at the Coral Gables Waterfront Communities HOA Board meeting, where a neighborhood representative is expected to brief the board on what residents have been seeing in the water.
The meeting is scheduled for Aug. 20 from 5 to 6:30 p.m.
With sargassum volumes exceptionally high across the broader region and Southeast Florida still vulnerable to additional beaching and accumulation, conditions in Gables by the Sea may not be the last Coral Gables waterfront residents see this season.
Excellent, Factual and Historically accurate article Gazette!
There’s also some potential beneficial use harvesting sargassium as a source for fertilizers and synthetics which Coral Gables can look into it given the massive cyclical quantities alongside our shorelines
We’re looking forward to “making something out of nothing”
Excellent and informative article.
THANK YOU!
JRH
Great informative article provided.
Every resident is well aware of the nasty sargassum environmental issue that unfortunately (seasonally) occurs daily on all the beaches located throughout Miami Dade, south Florida which I as a resident / taxpayer do not understand why this cleanup issue cannot simply be PROACTIVELY addressed and properly mitigated by City and County administrators with a proposed 2 cleanups occurring daily early am, and mid aft hours x 7 days on ALL of the public beaches and applicable waterways located throughout Miami Dade which with the proper equipment can easily be performed. This sargassum environmental issue has undoubtedly been adversely impacting marine life which has undoubtedly created a decline occurring in the local economy pertaining to visitor travel tourism industry hotels, restaurants, bars and retail stores.
I understand this environmental sargassum issue cannot be completely eliminated however with the proposed installation of highly visual netting above the water level line attached to many of existing floating buoys that are located several hundred feet offshore along the beaches in many areas throughout the County that are currently (primarily utilized to forewarn boaters, jet skis operators in order to deter them from hopefully traveling near the shoreline and potentially colliding with swimmers) it would serve to retain “the grand majority of the sargassum incoming onto the beaches on a daily basis.”
Please note that, even with the proposed netting installed offshore in the water ( 2 ft over the water line) on some windy days with rough and high tide surf conditions that are seasonally encountered there is always the potential for some of the floating sargassum material to potentially go over the proposed highly visual netting installed nevertheless I do currently believe this would only be occurring on a periodic basis which the quantity of incoming floating sargassum would be much less or nowhere near the current volume of sargassum currently landing daily on all of beaches throughout the County.
The initial cost involved to purchase and install the proposed netting attached to many of the existing floating buoyed markers located offshore along the beaches I believe would provide the County with an annual long term cost savings by deferring some of the daily clean up and disposal costs which are currently being incurred daily for this environmental marine toxic waste material. The proposed netting would also serve to maintain the beaches cleaner for All residents and visitors to enjoy as well as much SAFER as well by deterring potential sharks that maybe potentially encountered and would also serve to benefit the local tourism economy.
By removing the sargasum from the beaches, it could become fertilizer.