Long before the Florida Turnpike or Interstate 75 connected the state’s growing metros, manatees had their own tunnel system allowing them to shimmy from the Keys all the way to Georgia: rivers.
The chunky marine mammal is in dire straits these days, listed as threatened under the Endangered Species Act, the federal law that directs the U.S. Fish and Wildlife Service to protect and help bring back imperiled species.
In one of the country’s fastest-growing states, the gentle animals face a familiar list of threats including habitat loss, boat collisions, poaching, pollution and starvation as their seagrass food source vanishes from the coasts. However, the alteration of wild Florida’s waters threatens the manatees in lesser-known ways: through dams and locks that divide ancient river highways across the state.
SPECIAL REPORT: Dam Love Affair
In 2022, state biologists recorded the most manatee deaths caused by water-control structures since they began keeping records in 1974, according to the Florida Fish and Wildlife Conservation Commission’s manatee mortality database.
Researchers documented 19 deaths at nine different structures across the state that year. The animals were found crushed, trapped or drowned in dams and locks. Scientists said it would have been worse if at least 11 live manatees weren’t successfully rescued and released.
“Because of those mortalities, modifications are being made to reduce that in the future,” said Monica Ross, director of manatee research and conservation at the Clearwater Marine Aquarium.
Through November 2024, biologists had already recorded 17 manatees killed by dams and locks.
Despite the alarming numbers, Ross said those in charge of opening and closing Florida’s navigational locks are keenly aware of manatee passage. The concrete barriers are sometimes relics of the Cross Florida Barge Canal, a failed project to carve a passage across North Central Florida between the Gulf of Atlantic, under construction between the 1930s and 1960s.
Still, manatees find a way. The animals tagged by Ross and her team in the Ocklawaha River, the flow of which is thwarted by the Rodman Dam, go back and forth between locks without much difficulty, she said.
“It's pretty amazing — you’ll have animals that’ll line up on either side, waiting for a lock to open,” Ross said. “They have a routine.”
Spawning no more
While rotund manatees may be easy for lock managers to spot, dams pose an often untold threat to what are known as anadromous fish. These are fish that travel from the sea into freshwater rivers to lay their eggs, where they spawn.
Dams can severely limit the potential spawning areas of these fish, sometimes pushing species to the brink of extinction, said research scientist Steven Sammons, who runs a fisheries lab at Auburn University.
Alabama shad, for instance, could make their way up to Columbus, Georgia, if not blocked by the Jim Woodruff Dam on the Florida-Georgia border along with the three subsequent locks. There are historical reports of Alabama shad spotted all the way in Ohio prior to dams erected on the Ohio River, Sammons said.
In the early 2000s, the lock on the Apalachicola River was neglected, retired and fell out of use, and the shad’s numbers declined, too. The U.S. Army Corps of Engineers eventually decided to open the lock three times a day during the migration season, Sammons said — an early example of “conservation locking.”
“The implication is that if they can't access those areas, the population is going to be about 10% to 15% of what it could be,” Sammons said.
Fish passage can be expensive, costing millions of dollars to manage locks for aquatic animals or alter the structures to allow them to swim through.
Still, Bipartisan Infrastructure Law funds are encouraging many of these projects across the country, including in Florida. Every project looks different.
“Getting fish around man-made structures is not a one-stop shop,” Sammons said.
On the border of Wyoming and Utah, the Bear River cutthroat trout will soon be able to swim around an old dam, restoring more than 44 miles of river habitat. In the headwaters of Chesapeake Bay in the northeast, a series of 17 fish ladder installations, dam removals and culvert extractions will strengthen brook trout populations. In Washington, the federal government will work with the Cowlitz Indian Tribe to remove a weir on the West Fork Grays River — a benefit to winter steelhead, coho salmon, fall Chinook and chum salmon.
While some of the country’s rivers may never flow freely again, scientists say many can — and marine life may be better for it.
This story is part of a special project investigating dam safety in Florida from the University of Florida College of Journalism and Communications, supported by the Florida Climate Institute.
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