A stretch of the Ohio River near Pittsburgh remained closed to maritime traffic on Monday as crews equipped with sonar looked for a barge believed to have sunk over the weekend -- one of more than two dozen barges that broke loose and floated down the river.

The U.S. Coast Guard launched an investigation into how 26 river barges got loose from their moorings late Friday, striking a bridge and causing extensive damage to a marina. All but three of the barges were loaded with coal, fertilizer and other dry cargo.

No injuries were reported and no hazardous materials spilled into the river, according to Pittsburgh police and Coast Guard officials.

The area had been hit by flooding after heavy rains Thursday, and Coast Guard investigators were looking at high water as a possible cause or factor, said Cmdr. Justin Jolley of the Coast Guard marine safety unit in Pittsburgh.

One of the loose barges struck the Sewickley Bridge on Saturday afternoon. The bridge was closed at the time. An inspection revealed no significant damage, and the bridge was reopened to traffic, according to Steve Cowan, of the state Department of Transportation.

Eleven of the barges were pinned against the river bank and contained by a tugboat, while nine were secured at the Emsworth lock and dam downstream. The remaining barges went over the dam, and one remained unaccounted for on Monday.

"We're optimistic we'll be able to locate where that barge is today or tomorrow and then we can mark it accordingly and restore navigation," Jolley told The Associated Press.

Officials were working on a salvage plan to recover the other barges.

The barges were owned or operated by Campbell Transportation Co. Officials with the company were on site Monday morning and were not immediately available for comment.

"I think we were very fortunate given the circumstances here that there were no injuries or threats to life, no pollution and so far no major reports of damage to infrastructure to Army Corps locks and dams," Jolley said.

Peggy's Harbor, a family-owned marina on the Ohio River in Pittsburgh, sustained significant damage. A woman who answered the phone at Peggy's declined comment.

American Waterways Operators, a trade group that represents tugboat and barge companies, said it's awaiting the completion of the probe to "gain further insight as to what occurred." It said Monday that barges "safely and efficiently" move 58 million tons of cargo on Pennsylvania waterways each year.