The U.S. Fish and Wildlife Service is calling a manatee die-off in the ailing Indian River Lagoon an Unusual Mortality Event. 

The designation will prompt a federal investigation into why the manatees are dying.

More than 400 manatees have died in Florida since the start of the year, with at least 30 percent of those in the Indian River Lagoon.

That’s about triple the normal number. The average annual death count during the past five years had been just under 600 manatees. 

The manatees are believed to be starving, as recent harmful algae blooms in the Indian River Lagoon have led to a widespread loss of seagrass, the manatees’ primary food. 

The designation of an Unusual Mortality Event also will prompt the federal government to look into how to minimize more deaths. 

The manatee was reclassified in 2017 as threatened rather than endangered. Some 7,000 of the animals are believed to be in Florida. 

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