The Indian River Lagoon: 156 miles of estuary, and what the blooms did to it

The Indian River Lagoon is a 156-mile estuary along Florida’s east coast, and much of it runs through Brevard County. Florida Atlantic University’s Harbor Branch Oceanographic Institute notes that it has been cited as among the most biologically diverse estuaries in North America. It is one of 28 estuaries the federal government has designated Estuaries of National Significance. Six counties, from Volusia south through Brevard to northern Palm Beach, lie in its watershed, and five inlets through the barrier islands connect it to the Atlantic. Those inlets are natural in origin, the university says, but have been stabilized and are kept open by people.

What lives in it

The numbers are large. Harbor Branch counts more than 2,100 plant species and more than 2,200 animal species in the lagoon’s watershed, including some 700 fish and 310 birds, and about 50 species listed as threatened or endangered. The university attributes the diversity partly to geography, since the lagoon straddles a warm-temperate climate to the north and a subtropical one to the south, and partly to its distinct habitats, foremost among them seagrass meadows, mangrove forests and salt marshes.

The 2011 superbloom

The lagoon’s worst modern year began in the spring of 2011. The St. Johns River Water Management District recorded a massive phytoplankton bloom and loss of seagrass that spread, from early spring through late fall, through most of the lagoon from southern Mosquito Lagoon to just north of Fort Pierce Inlet. Its scientists wrote that it “far exceeded any past events remembered or documented” in geographic scale, intensity, duration and seagrass loss.

The worst of it, which they named the superbloom, covered about 53,000 hectares, roughly 130,000 acres, of the Banana River Lagoon, the southern Mosquito Lagoon and the northern Indian River from Eau Gallie north. By the end of June 2011, seagrass beds there and in the central lagoon had shrunk by about 45 percent from the summer before, a loss of roughly 31,600 acres against the 70,230 acres mapped in 2009, and the district expected the year’s total to be higher. It put the potential cost to commercial and recreational fisheries at $150 million to $320 million in 2011 and 2012.

The cause wasn’t obvious. The years 2009 to 2011 were dry, and treated wastewater discharges had been falling, so the usual route for nutrients, rainfall runoff, was running low. The district’s 2012 plan suggested the bloom may have been fed mainly by nutrients released from within the lagoon itself.

The years that followed

Brevard County’s 2026 ordinance renewing its lagoon sales tax lists what came after: brown tides in 2012, 2013 and 2015; unusual mortality events for dolphins, manatees and pelicans; and, from January through March 2016, “the most extensive and intensive algal bloom ever recorded in the Indian River system during winter to spring months,” followed by one of the most extensive fish kills ever recorded in the county when it collapsed.

The manatees

The seagrass losses eventually starved the lagoon’s manatees. The Florida Fish and Wildlife Conservation Commission records an Unusual Mortality Event on the Atlantic coast from December 1, 2020, to April 30, 2022, in which 1,255 manatee carcasses were documented and 137 manatees rescued. State and federal investigators determined the cause was starvation from a lack of forage in the Indian River Lagoon; 1,039 of the deaths came in the two winters, when cold added to the stress. The FWC and the U.S. Fish and Wildlife Service fed the animals at least 600,000 pounds of leafy greens over the winters of 2021-22 and 2022-23. The last starvation death was documented in March 2023, and the event was closed on March 14, 2025, as seagrass slowly came back in some key areas.

The response in Brevard

Brevard’s voters answered with a tax. On November 8, 2016, after the winter bloom and fish kill, they approved a half-cent sales tax for ten years, 2017 through 2026, to pay for the county’s Save Our Indian River Lagoon plan, and every city and town in the county signed on. The county describes the work as reducing pollution, removing legacy nutrient loads such as muck, and restoring natural filtration, and the plan is updated every year with a citizen oversight committee. With the tax due to expire, a ten-year renewal went on the November 3, 2026, ballot.

How the bloom looked from one city on the lagoon is on Old Titusville’s lagoon page.

Further Reading

• Florida Manatees: Biology, Behavior, and Conservation by John E. Reynolds III
• Florida’s Fabulous Natural Places by Tim Ohr