News

By Dr. Beth Brady, Director of Science and Conservation

This year, Manatee Appreciation Day brought a hopeful milestone: the official end of the Unusual Mortality Event (UME) that devastated Florida’s east coast manatee population. The UME, which lasted from December 2020 through April 2022, was the deadliest on record, resulting in 1,255 manatee deaths. Most occurred during the winters of 2020-21 and 2021-22, primarily along Florida’s Atlantic coast.

The event was driven by widespread seagrass loss in the Indian River Lagoon (IRL), where a series of harmful algal blooms over decades destroyed more than 90% of seagrass biomass. The blooms were fueled by excessive nitrogen and phosphorus pollution from leaking septic systems, inadequately treated sewage, fertilizers, and stormwater runoff. Eventually, the blooms became so large and frequent that the algal growth blocked out sunlight and killed the seagrass beds in the IRL. This eutrophication cut off a vital food source for manatees. Many of the carcasses found during the UME showed signs of severe emaciation.

In 2021, the Working Group on Marine Mammal Unusual Mortality Events confirmed the spike in manatee deaths met the criteria for a UME, prompting the U.S. Fish and Wildlife Service (FWS) to issue a formal declaration. Since 1991, there have been nine manatee UMEs, but this was the most severe. A 2013 UME, also linked to forage loss in the IRL, led to a toxic infection caused by a dietary shift and resulted in the death of 111 manatees. This event foreshadowed the more severe crisis that would later unfold in the lagoon.

During the 2020-22 event, the Florida Fish and Wildlife Conservation Commission (FWC), FWS, and partners rescued 137 manatees. After April 2022, deaths and rescues declined, but monitoring, habitat assessments, and rescue efforts continued. This ongoing work was supported in part by increased funding and staffing provided to FWC to aid in recovery efforts.

Today, mortality rates have returned to pre-UME levels. Recent health assessments in Brevard County (where much of the IRL is located) show manatees have improved their physical condition. Researchers have seen more cow-calf pairs as well as a higher rate of stillborn calves, suggesting that female manatees are consuming enough food to be able to sustain a pregnancy.

While there has been a slight increase in forage in some areas, manatees are still in danger. The root causes of seagrass loss must be addressed to sustain even the small gains seen on Florida’s east coast. Statewide, seagrass acreage continues to decline—in places like Biscayne Bay, the Panhandle, parts of Tampa Bay, and the St. Johns River—driven by the same environmental stressors as those seen in the IRL. A Tampa Bay Times article from April 12 reported that one in four Florida waterways are polluted with nitrogen, phosphorus, or other chemical imbalances.¹ Climate change is compounding these threats: a recently published article suggested sea level rise is projected to cause a 34% loss of seagrass in the Indian River Lagoon by 2050,² and increased hurricane activity has led to saltwater intrusion, especially along Florida’s west coast. In just the past two years, 10 manatees have died from eating macroalgae, likely due to a loss of eelgrass, their main food source.

Recently, a federal court ruled that the Florida Department of Environmental Protection violated the Endangered Species Act by permitting wastewater discharges into the IRL. The state is now required to seek a federal permit to help reduce future harm to manatees and their habitat. Even with the ruling, it could take more than a decade for legacy pollutants already in the lagoon to clear. While the timeline is daunting, the ruling does offer hope by holding the state accountable for failing to address the root causes of water pollution.

Although the UME has officially ended, manatees and their habitat remain under threat. Funding for the comprehensive restoration of the IRL must be vastly increased and accelerated by both the federal and state agencies if catastrophic losses of seagrasses and imperiled manatees are going to be avoided in the future. Manatees are more than a species in peril—they are a sentinel for ecosystem health. Their survival is directly linked to the quality of the waters we all depend on. Protecting manatees means protecting the future of Florida’s environment—and ensuring a future for all who call this place home.

References
¹Sampson, Z. T., Barnes, B., & Vuttaluru, S. (2025). Florida waters are getting more polluted. Here’s what the Times found. Retrieved from https://www.tampabay.com/investigations/2025/04/12/florida-water-pollution-algae-bloom-seagrass-manatees-springs/
²Parkinson, R.W., Juhasz, L., Wdowinski, S. et al. Sea level rise submergence simulations suggest substantial deterioration of Indian River Lagoon ecosystem services likely by 2050, Florida, USA. Reg Environ Change 25, 54 (2025). https://doi.org/10.1007/s10113-025-02389-7