The crash occurred during a training flight.
Rescue crews initially recovered both aviators from the water and transported them to the Lower Keys Medical Center, but the Navy later tweeted that the flyers did not survive.
“We are sad to report that both aviators have been declared deceased. Their families are in our prayers,” the Navy said on Twitter.
The F-18 crew was based out of the U.S. Naval Air Station Oceana in Virginia Beach and was on a final approach to Boca Chica Field when the crash happened.
Witnesses reported what appeared to be a mid-air explosion, according to the Florida Keys News.
"I saw the fire and then it just dropped," Barbie Wilson told the news outlets.
Wilson said the plane seemed to turn on its side before bursting into flames.
“In the air, I saw fire,” she said.
There’s not word on exactly what caused the crash, but the Navy is investigating.