Authorities are searching for a missing man who was stranded on an island in the Chattahoochee River near Johns Creek.

Channel 2 Action News reports that authorities executed a water rescue Monday evening after five people were stranded on the island, located at the Chattahoochee Recreational Area on Barnwell Road.

The Fulton County Fire Department said four people were recovered during the rescue. Gwinnett County, Roswell and Johns Creek officials are searching for the fifth in boats, according to Channel 2. Crews are using sonar and a helicopter equipped with infrared to attempt to locate the missing man, said to be in his 20s.

Gwinnett Capt. Tommy Rutledge said there was a water release from Buford Dam around the time that the man disappeared. The water level can rise from six to 11 feet during that release, he said.

Authorities are not sure this is what caused the man’s disappearance, but it would have created conditions to sweep him away, Rutledge told Channel 2.

The Johns Creek Fire Department is now in charge of the case, with an assist from Gwinnett.

No other information was immediately available.