Three construction workers were presumed dead Wednesday after falling 100 feet from a highway bridge into the swollen Arkansas River, authorities said.

The men were working on installing 30-inch-diameter waterlines under and across the Interstate 430 bridge when their scaffolding platform collapsed, officials said.

The rescue operation turned into a recovery effort when there was no sign of the men for more than an hour after their fall, Little Rock Fire Capt. Jason Weaver said. Divers could not enter the water because the current was too swift.

Charles Jackson, a worker on the project, said he'd been on the platform earlier in the day and noticed no safety problems. He said he knew the three missing men well.

Jackson said that, if the men were tethered to the platform for safety they would be able to get unhooked.

Recovery crews hooked what appeared to be the fallen scaffolding, but the structure weighed as much as 10,000 pounds and officials decided to close northbound lanes of the interstate so they could bring in a heavy-duty crane.

The platform was big enough to hold the men, two generators and a welding machine, Weaver said. "A lot of metal, a lot of weight," he said.

Central Arkansas Water utility spokeswoman Marie Crawford said the men worked for Renda Contracting Inc.

Corey Wells, treasurer and controller for Renda Contracting of Roanoke, Texas, said the company was contacting the workers' families.