By Coral Gables Gazette staff

Beachgoers hoping to enjoy Coral Gables’ picturesque Matheson Hammock Park atoll pool received an unpleasant surprise earlier this month when more than 100 dead fish floated to the surface of the popular swimming area, with many washing up along the shoreline.

The incident occurred June 13 and was captured in a video later shared by environmental advocacy group Miami Waterkeeper. The footage showed dead fish scattered along the edge of the atoll pool and adjacent beach area.

Testing continues before reopening

Matheson Hammock is a Miami-Dade County park, and county officials confirmed this week that the atoll pool remains closed while additional water quality testing is conducted.

“Yes, it is still closed,” said Ivan Castro, communications and marketing chief for Miami-Dade County, on Monday. Castro said county officials were awaiting the results of new water tests and hoped to reopen the pool as soon as conditions allow.

Castro said he was not initially aware of the fish kill event itself but confirmed that testing by the Florida Fish and Wildlife Conservation Commission and Miami-Dade County’s Department of Regulatory and Economic Resources found unusually low oxygen levels in the water, a condition that can trigger fish deaths.

He emphasized that testing did not reveal dangerous levels of fecal contamination or harmful bacteria.

“It was just in an abundance of caution that we decided to close the pool,” Castro said.

Low oxygen suspected

Matheson Hammock is no stranger to temporary closures. The atoll pool, which receives water directly from Biscayne Bay through two openings, has periodically been shut down in the past because of elevated bacteria levels. Its shallow waters can also become vulnerable to low oxygen conditions, particularly during periods of high temperatures and limited water circulation.

According to county officials, the recent closure differs from previous incidents linked to bacterial contamination. Instead, investigators believe oxygen depletion likely caused the fish kill.

The county continued conducting water testing this week and planned to reassess conditions before reopening the swimming area.

Miami Waterkeeper, which posted the video of the fish kill on its Facebook page, urged residents to report similar environmental incidents.

“Over the weekend, our team was informed of a fish kill event at Matheson Hammock Park,” the organization wrote. “Every report makes a difference. Thank you for helping protect the water you love.”

A historic county park

Located along Biscayne Bay in Coral Gables, Matheson Hammock Park holds a unique place in Miami-Dade County history. According to county information, it was the county’s first park and is home to the county’s second-largest publicly operated marina. The marina accommodates approximately 330 vessels and includes boat ramps, fuel docks, dry storage facilities and a Miami-Dade Sheriff’s Office Marine Patrol station.

The man-made atoll pool remains one of the park’s most popular attractions, drawing families and visitors seeking calmer waters than those typically found along South Florida’s open beaches.

Broader water-quality concerns

Water quality concerns have become increasingly familiar at several Miami-Dade recreational beaches. Just weeks before the Matheson incident, the Florida Department of Health issued a health advisory for Crandon Park North on Key Biscayne ahead of the busy Memorial Day weekend after testing found elevated levels of Enterococcus bacteria, which can indicate fecal pollution.

Health officials warned swimmers to avoid water-related activities because exposure to elevated bacteria levels can increase the risk of illness, infections and skin rashes. Sources of such contamination can include stormwater runoff, wildlife, pets and sewage.

County officials stressed that no such bacterial contamination has been detected at Matheson Hammock during the current closure. Instead, they continue to monitor oxygen levels and overall water quality while awaiting final test results before reopening the atoll pool to the public.