BILLINGS, Mont. - Emergency workers ferried supplies to more than 300 people cut off Friday by flooding that has overwhelmed Montana towns and caused an estimated $8.6 million in damage.

Heavy rain and the runoff from record mountain snowpack have caused rivers over much of the West to spill from their banks. Montana has been hit particularly hard over the last few weeks, with hundreds of homes inundated and scores of roadways swamped.

River levels were retreating throughout the state Friday, but more rain this weekend was expected to cause floodwaters to linger across southeastern Montana.

There, roads washed out by the raging Musselshell River left people in a sprawling rural neighborhood in the hills outside the town of Roundup with no way to get out.

Stranded residents were able to call in grocery orders that emergency officials delivered by boat, said Cassie Degner, a local volunteer firefighter. A trailer filled with water, diapers, and other essentials had been brought into the neighborhood before access was lost Wednesday.

Mary Brower, 81, said she had not been able to get into town since May 20, and roads have further deteriorated since then. "They're going to bring in my medications today by, I don't know, rowboat or whatever," said Brower, who suffers from congestive heart failure.

Up the road from Brower, rancher George Smith said he and his wife, Loris, were rationing gasoline but otherwise planned to get by with "a few cans of different stuff we have on hand."

Authorities in Roundup began pumping out a portion of the downtown that has been swamped twice since the Musselshell started to rise in late May. Workers also scrambled to rebuild a makeshift dike along the edge of town that was overtopped and severely eroded earlier in the week.

Gov. Brian Schweitzer estimated the flooding had caused more than $8.6 million in damage across the state since the end of May.

That figure was included a letter Thursday to President Obama in support of a previous request for a disaster declaration. Schweitzer's office said it could rise with additional damage. The request for federal assistance covered 31 Montana counties and four Indian reservations.

The melting snow and rain caused the Army Corps of Engineers to release water from the Fort Peck Dam into the Missouri River at a record 60,000 cubic feet per second. That sent torrents of water gushing downstream, flooding low-lying areas of the Fort Peck Indian Reservation and adding to flood pressures in North and South Dakota.

The U.S. Department of Agriculture said Friday it would provide $600,000 each to Montana, Colorado, Idaho, Utah, and Wyoming for emergency restoration projects.