Manatees are no longer an endangered species and have been reclassified as “threatened”.
The numbers of the aquatic mammals - sometimes known as sea cows - in Florida had fallen to just a few hundred in the 1970s but has now reached more than 6,600.
Under the "threatened" classification, manatees are still considered likely to become endangered within the foreseeable future. An "endangered" listing means that a species is in danger of extinction.
Significant steps have been taken over the last 30 years to ensure manatees are no longer endangered, including speed limits on boats to prevent collisions and redesigns of locks and levees.
Phil Kloer, spokesman for the US Interior Ministry’s Fish and Wildlife Service said this was a “success story”.
"It has been doing very well, it has been coming back," Mr Kloer said.
The move to take sea cows off the list has faced criticism from conservationists who have argued it weakens protection for the animal.
Frank Jackalone, director of the Florida chapter of the Sierra Club, criticised the decision and said local and state authorities would now ease boating rules.
"Florida boaters are going to take this as a signal that they can increase their speed in manatee zones," he said.
Florida state numbers show 520 manatees deaths last year, 104 of them from watercraft.