Dover said he knew something had gone wrong when he saw the Oklahoma Highway Patrol and other emergency vehicles.
The boats collided during the High Roller Poker Run on Saturday. Four people died at the scene and two were flown to the hospital, where one later died, according to the patrol.
"There was just floating debris,'' Dover said. "We've seen life vests, we've seen life preservers.''
Two couples were on one boat, while a third was on the other, trooper Kera Philippi said. One of the boats struck the other on the middle of its side.
The victims were identified as Ann, 59, and Gordon Mineo, age unknown, of Rockwall, Texas; Amy Dawn, 31, and Justin R. Lane, 25, of Little Elm, Texas; and Myra L. Gibson, 51, of Old Hickory, Tenn.
Gibson and her husband, Bruce, 54, were flown to a Dallas hospital, Philippi said. Bruce Gibson's condition was not known.
Philippi said Gordon Mineo was the organizer of the poker run, in which participants get a playing card at each of five different stops along the lake and then compare their cards at the end of the game. The team with the best poker hand wins.
"They were still involved in the poker run when the accident took place,'' she said.
Only pieces were left of one boat. The rear of a yellow, twin-hull jet boat with purple trim was partially submerged and the left side of the bottom was ripped out. A tugboat towed the damaged boats to shore, Philippi said.
Troopers won't able to determine the cause of the accident until a reconstruction of the boats and the event are done, which could take several days, she said.
Labor Day vacationers remained at the shore of the massive lake, which is Oklahoma's second-largest body of water and straddles the Oklahoma-Texas border. But the mood was somber.
"We just kind of held our heads down and came back in and are just waiting to hear what really did happen,'' Dover said