Unseen Peril: Coconut Grove’s Coastal Waters in Steep Decline

Like the rest of Biscayne Bay, Coconut Grove’s marine ecosystem faces mounting challenges from pollution, outdated infrastructure, and the false belief that all is well beneath the surface.

Kenny Broad remembers when Biscayne Bay’s shallow waters teemed with fish, lobsters scurried across the seafloor, and simple flat-bottom skiffs were the vessel of choice.

“It was sort of a peaceful place of refuge,” says Broad, a North Grove resident who moved to the area in the late 1960s. “A place to get away from the city.”

But the Biscayne Bay of today, says Broad, Director of the University of Miami’s Abess Center for Ecosystem Science and Policy and a former National Geographic Explorer of the Year is, in many ways, unrecognizable from the paradise of his youth.

Fish populations are plummeting, seagrass beds are dying, and sewage and other pollutants are often so high within coastal waters that swimming is unsafe.

“I call it an ecological crisis that is unfolding in the bay” says Audrey Siu, the policy director of Miami Waterkeeper, a marine-focused environmental advocacy group. “I think we’re at a tipping point where if we don’t take drastic and sustained action our bay is going to be forever changed.”

And the importance of Biscayne Bay, Siu notes, extends far beyond its natural appeal: A 2023 study reveals that marine-related commerce and activities within the bay create nearly 450,000 jobs, and contributes about $64 billion annually to Miami-Dade’s economy, representing about 19 percent of all economic activity.

“The bay is what makes Miami, Miami,” says Siu. “The bay and our beaches and our reefs are what distinguish us from other big coastal cities in the country.”

Coconut Grove’s coastal waters, despite their importance to the community’s branding as a nature-filled playground, are not immune to the afflictions degrading the bay.

Since 2019 when county officials began rating the overall water quality at locations around the bay, the Coconut Grove area has never received a rating above “fair.” And once, in 2021, it received the lowest rating of “poor.”

The only one of 12 sites monitored in the annual Biscayne Bay Report Card study which received a rating of “good” in 2024 was the area off Brickell.

The study looks at eight measurements to produce the ratings, including phosphorus and nitrogen – the nutrient pollutants most responsible for algae blooms and fish kills – and chlorophyll-a, which reveals how much algae is present. 

In 2024 the Grove’s waters received a “good” mark in total phosphorus, “fair” in total nitrogen, and “poor” in chlorophyll-a, indicating an overload of algae present in the water. Algae growth can cause myriad problems for the delicate South Florida marine ecosystems, hampering seagrass growth, depleting oxygen levels, outcompeting beneficial phytoplankton species and, in some cases, producing toxins harmful to other marine life and humans.

Phosphorus and nitrogen are chemical elements that can be found in everything from human effluent and fertilizers to organic matter (like plant debris) and enter the bay through stormwater runoff and leaky septic and sewer systems. In excess, they wreak havoc on the bay’s delicate ecosystem balance, particularly when it comes to seagrass, the lungs of the bay that provide oxygen for marine life to survive. 

Scientists say that together, phosphorus and nitrogen create a kind of snowball effect, fueling seagrass growth at exponential rates. But with insufficient levels of sunlight and oxygen to support this over-abundance, the seagrass beds die off entirely, adding even more decomposed nutrients to the bay. 

“In Coconut Grove and Coral Gables, we’re seeing an algal bloom that is not a microscopic algal bloom, but a macro algal bloom that you could see with your naked eye,” says Pamela Sweeney, Senior Manager of Miami-Dade County’s Division of Environmental Resources Management.

Seagrass provides critical habitat and food for a wide variety of marine life. Its loss impacts the entire marine ecosystem of the bay.

UM’s Broad describes the seagrass flats as the “metaphorical heart and soul” of the bay. “It’s not a surprise that the bay is dying if we wipe out the seagrass,” he says.

A 2018 study by Miami-Dade County (the most recent available) found that in the previous 13 years seagrass in the waters off Coconut Grove and Coral Gables declined by 84 percent.

Biscayne Bay’s once abundant seagrass beds are also imperiled by increased boat traffic. Viewed from above, the shallow water near Miami-Dade’s coastline appears crisscrossed with the scars of boat propellers that have torn through seagrass beds. 

Sweeney warns that bay waters in poor health may lack the resilience to withstand extreme events, both natural ones like hurricanes, and the manmade variety such as the massive fish kills in the northern sections of Biscayne Bay in 2021 brought on by a combination of warm weather and high levels of land-based nutrient runoff.

These looming threats are spawning a debate among scientists and policy officials on whether the rating standards within the bay’s annual report card of water quality should be tougher.

“We’ve had dialogue with the State of Florida [officials] over time to say, well, is phosphorus set too high for our bay?” says Sweeney, noting that areas of Biscayne Bay with “good” water quality ratings are still experiencing seagrass die offs, fish kills and other effects of nutrient overload.

High bacteria levels are another measure of poor water quality in Biscayne Bay, as indicated by the periodic beach closings, particularly in warm weather months, due to unsafe swimming conditions.

Miami Waterkeeper routinely measures for enterococci, a fecal indicator bacteria that reaches the bay through stormwater overflows, surface runoff and leaking septic systems.

Of the 20 measurements recorded at Peacock Park by Miami Waterkeeper since August, 50 percent exceeded the safe swimming standards set by state Health Department officials.

Much of South Grove remains dependent on aging septic systems that scientists warn will become even more vulnerable to leakage due to rising sea levels and increased seasonal rain events. 

Another contributor to Biscayne Bay’s overall decline is the increasing amounts of trash, especially plastic which breaks down into microplastics that can make their way into the marine ecosystem.

Like nitrogen, phosphorus and other nutrients, trash often makes its way into the bay through our stormwater system. In theory, catch basins strain out trash and other sediments such as grass clippings before they reach the bay. But Miami’s aging systems have proven largely ineffective at halting the flow.

“[Catch basins] were designed before plastics were really prominent, and so the stormwater systems are really a very significant conduit for both plastics as well as nutrients,” says Dave Doebler, founder of VolunteerCleanup.org, a group that organizes coastal cleanups along Miami-Dade’s shoreline and lobbies for better pollution control measures.

Catch basins must be cleaned regularly, Doebler explains, otherwise trash can overflow or bypass the system. The City of Miami cleans its basins every other year, Doebler says, despite U.S. Environmental Protection Agency recommendations they be cleaned twice annually. Investments in new technology would also help, he says.

Coconut Grove’s most visible example of the county’s antiquated stormwater system can be seen by the Seminole Boat Ramp where SW 27^th Avenue meets the bay. While manatees frequently visit the site to drink from the steady stream of fresh water, the screening grate at its mouth is packed nearly solid with plastic bags and other debris.  

Despite the mounting threats to marine health, a survey of more than a thousand Miami-Dade residents in 2022 found that most people considered Biscayne Bay to be “moderately healthy” – a stark contrast to the annual report chronicling the declining water quality.

That disconnect between perception and reality worries Broad, who says even quite subtle, almost imperceptible changes in the environment can be “very dramatic from a biodiversity and ecological standpoint.”

Broad argues that the science documenting the bay’s decline is both plentiful and irrefutable. The real battle is convincing people to care. Coconut Grove, often painted as a kind of subtropical Eden with its lush tree canopy and calm waters, is a microcosm of Miami’s environmental paradox, he says. 

“The Grove’s environmental ethics seems to be diminishing,” Broad says. “I think in part, because it’s a population now of people coming in that don’t have the same sort of historical roots.”

Siu, a Miami native, remembers hearing her parents express dismay that coastal waters once reliably “Caribbean blue” had become progressively murky, less supportive of marine life.

“We need to generate awareness of what the bay’s ecological baseline used to be, maybe decades ago,” Siu says. “Getting folks to understand that what we’re seeing now is not normal.”