Beaufort County Sheriff's Maj. Bob Bromage told The Associated Press the family found the cocaine, worth more than $600,000, on Fripp Island, where they were staying at a rental house.
They spotted a trash bag in the water, Bromage said, and brought it to shore, loading it onto a golf cart. Back at the rental, they cut into it and found brick after brick of a white substance.
They then called authorities for help.
Bromage said that he believes Hurricane Dorian may be to blame for the discovery of the drugs, saying he believes they were pushed close to shore in the storm.