The Sandusky Register reported witnesses said the boat, carrying seven people, slid backward down the lift hill and flipped into the water at 6:42 p.m.
"All seven guests on the boat were transported to Cedar Point's first aid station," the amusement park said in a statement. "Six of the guests were evaluated and treated by Cedar Point EMS staff and released. One guest was transported to Firelands Regional Medical Center in Sandusky, Ohio, for additional evaluation."
The cause of the accident was under investigation and the Shoot the Rapids ride will remain closed until park officials and state inspectors complete their review, park officials said.