Updated

One day after a bridge collapse killed several people on a major east-west Interstate, recovery crews pulled a fourth corpse from the Arkansas River Monday.

However, divers were forced to halt the search when the threat of lightning made it too dangerous to continue.

Authorities said several vehicles remained underwater from Sunday's collapse of the Interstate 40 bridge over the murky, swiftly flowing Arkansas River. They expected to recover more bodies as divers reached more vehicles in the water.

The dive was suspended early Monday as a thunderstorm moved into the area. Rescuers were using sonar to map the debris field and were bringing in cranes to lift chunks of the bridge and vehicles from the water.

Divers were not planning to return to the river until Tuesday morning, said Highway Patrol Lt. Chris West.

The bodies of three women and one man were recovered by Monday. At least five people escaped with injuries when a 500-foot section of the nearly 2,000-foot bridge was sheared off.

The accident occured when Joe Dedmon, the 61-year-old pilot of a towboat pushing two barges side-by-side, apparently blacked out at the helm, said Joel Henderson, a spokesman for Magnolia Marine Transport Co., which owns the boat.

Dedmon appears to have passed out for about two minutes and was unable to steer the barges through the river channel under the bridge, Henderson said. Nobody was on hand to take the helm from him.

Preliminary tests on the captain showed he had not been using alcohol or drugs. Dedmon regained consciousness after the collision but remained hospitalized Monday pending further tests.

"He's just terribly distraught and shook up about the incident," Henderson said.

Divers weren't able to see anything in the deepest parts of the churning river, and resorted to feeling their way around twisted steel in search of vehicles. Terry Stephens, coordinator of the Highway Patrol's dive team, said mangled cars were piled on top of each other.

Rescuers were using sonar to map the debris field and were bringing in cranes to lift debris from the water.

Kay Blanford of Southerland Springs, Texas, feared two of her friends went off the bridge while hauling a trailer loaded with four race horses. Rescuers hadn't found her friends but pulled three dead horses out of the river. Blanford was following in another car but got caught in a traffic jam.

"I've been trying to call them on the cell phone and they still haven't answered," she said.

The barge was moving upstream and about 300 feet outside the regular navigation channel when the accident happened, a U.S. Army Corps of Engineers spokesman said.

Huge rock-filled bumpers protect bridge supports near the navigation channel from boats or debris moving downstream, but the columns are not protected from vessels moving upstream, said Dennis Johnson, the corps' area manager.

He said it is unusual for a barge to hit a bridge while moving upstream outside the channel.

"This is just one of those things," Johnson said. "I don't know how you could have prevented it."

The empty, 490-foot barge, longer than a football field, was going about 5 mph when it hit the span. Alongside it was the second barge of the same size. The width of the two barges together was 108 feet.

The channel is about 300 feet wide under the bridge, Johnson said. The barge missed the channel by about 300 feet and slammed into the columns supporting the bridge at its west end. The columns were destroyed.

Investigators will try to determine if there was anything wrong with the bridge, built in 1967, to explain why the accident caused the roadway to collapse, said George Black, a spokesman for the National Transportation Safety Board. The bridge passed an inspection a year ago.

At the accident site, a crane hoisted a victim's car from the water shortly after divers resumed the search at daybreak Monday.

The names of the four dead have not been released. Among those who escaped the collapse with injuries was James Bilyeau, a truck driver from Conway, Ark., who was pulled from water by two fishermen competing in a bass tournament nearby.

"He was in really bad shape. I don't know how he hung on like he did," said one of the fisherman, Randy Graham. "I said, 'You're all right. We got you."'

Bilyeau, who remained in a hospital Monday with head injuries, telephoned the other fisherman, Norman Barton, on Sunday night, and "he kept saying over and over, 'You saved my life,"' Barton said.

Relatives at Webbers Falls City Hall waited for news of their loved ones.

Wayne and Susan Martin never showed up at a family reunion in Clarksville, Ark., and their daughters haven't been able to reach them on their cell phone.

Their relatives said they feared the couple, traveling in a pickup truck, fell to their deaths.

"He was my baby brother," Gwen Smith said. "We have not had contact with them."

The Associated Press contributed to this report.