LIVINGSTON, Mont. - A bridge over the Yellowstone River that links two islands with the town of Livingston is still in danger of collapsing, Park County Sheriff Allan Lutes said Sunday.

But crews are continuing to construct a "Bailey bridge" - a type of temporary metal truss bridge designed for use by the military - on top of the existing structure. And if all goes smoothly, vehicles should be crossing it in just a few days, Lute said.

Authorities closed the 180-foot Ninth Street Bridge on Thursday after a portion of it began to sag into the high, fast-moving Yellowstone. The one-lane bridge, built 44 years ago, is the only access to the 35 homes on Ninth Street and Siebeck islands, which are connected by a narrow causeway.

"The bridge is still standing," Lutes said Sunday. "But the part that's collapsing is still collapsing slowly."

Ten or so island residents left their homes Thursday, and another 16 were evacuated by helicopter Friday. Up to 20 island residents remained in their homes Sunday, and authorities were checking on them regularly, Lutes said. He added that those who stayed did so by choice.

"They can't go back and forth whenever they want, but we haven't abandoned them," he said.

A natural gas line attached to the bridge has been disconnected, but island residents still have power, water, phone lines and other amenities, Lutes said. In addition, police and emergency vehicles have offered to shuttle medications or other necessities to residents by boat or helicopter.

The river was still rising Sunday, but "there has been no serious flooding here yet," Lutes said, adding that no homes were threatened.

The Bailey bridge is expected to hold up even if the existing bridge collapses, he said. It will remain in place until authorities decide on a permanent solution.

Lutes added that any debris from a potential bridge collapse will sink, so people don't have to worry about downstream damage.

One of the bridge's concrete support beams sank nearly a foot on Thursday and Friday - after being pounded for weeks by the Yellowstone River, which flows through Yellowstone National Park and across much of southern Montana on its way to the Missouri River.

The bridge showed little change Saturday, but "the risk of a complete collapse still remains," Park County spokeswoman Kerry O'Connell said Sunday in a news release.

As of Sunday morning, the river was at 8.94 feet, according to the National Weather Service in Billings. Flood stage is 8.5 feet.

The weather service predicted the river may crest by noon Monday at 10.1 feet, the release said. The historical high is 10.72 feet recorded in 1997.

Ten feet is considered a major flood stage, according to the weather service's Advanced Hydrologic Prediction Service, which monitors river flows around the nation.

The high, faster water and bridge issues have prompted the Montana Department of Fish, Wildlife and Parks to close the river to all recreational use from Carter's Bridge to the bridge at U.S. Highway 89 North.