By Laura Zuckerman
SALMON, Idaho (Reuters) - Historic flooding in the Missouri River basin spurred voluntary evacuations in North Dakota on Monday, while in Montana emergency workers ferried food and water to a town cut off by flood waters.
The measures came as states in the northern Rockies and northern Plains plan for displacement of thousands and scramble to build levees in an expanding fight against river overflows predicted to worsen in coming weeks.
The crisis has caused governors in Montana, the Dakotas and Wyoming to call up hundreds of National Guard soldiers to bag sand and try to dissuade anxious property owners from navigating submerged roads and washed-out bridges.
"There's a whole heck of a lot of water everywhere," said Ed Tinsley, head of Montana Disaster and Emergency Services.
Rains in the region on Monday intensified threats already posed by melting of record snows in the Rockies, prompting federal water managers to increase controlled spills from mainstem reservoirs into the Upper Missouri River from Montana to states downstream.
The record releases are designed to ease pressure on six dams and prevent uncontrolled flooding that would place hundreds of thousands of people at risk, officials said.
Water as deep as eight feet kept the central Montana community of Roundup isolated on Monday. The town's 2,000 residents have been battling the Musselshell River, which breached its banks last week.
The state delivered 3,000 gallons of water to Roundup, where residents have been advised to boil water before drinking to avoid illness.
Authorities on Monday continued to deny rumors that the Fort Peck Dam in northeastern Montana had failed. Tinsley said the rumors had sparked panic among members of two Indian tribes and other residents of two surrounding counties.
In North Dakota, controlled releases from the Garrison Dam on the Missouri River above Bismarck reached record levels on Monday, with authorities going door-to-door in neighborhoods in the capital city and adjacent Mandan to encourage voluntary evacuations.
"We're in completely uncharted territory," said Cecily Fong, spokeswoman for the North Dakota Department of Emergency Services.
In north central North Dakota, flood waters from the Souris River caused damage to a sewer main in Minot, home to 40,000 people. Officials warned residents to plug drains and toilets in basements to prevent sewage from backing up into homes.
In nearby Burlington, the Souris, a tributary of the Red River, has waterlogged rural residences and wearied homeowners who have been in a weeks-long flood fight.
Charissa Sorenson and her family have spent $20,000 to build a fortress of sandbags around their riverside home.
"It's bad, it's really bad, but we're going to fight it out," she said in a telephone interview on Monday.
In South Dakota, Lieutenant Governor Matt Michels and additional National Guard troops were dispatched on Monday to two communities, Yankton and Dakota Dunes, in the southeastern tip of the state where some residents have evacuated in advance of likely flooding.
The deployment follows planned releases on the Missouri River that will reach all-time highs from a dam north of the capital city of Pierre and its sister city of Fort Pierre, where flood fortifications have been under way for days.
In Idaho, tributaries of the Columbia River have breached their banks in the eastern and northern parts of the state, prompting the governor to declare a state of emergency.
The high water in the Columbia and Missouri basins comes after major flooding already this year of the Mississippi River in the Midwest and south to the Gulf of Mexico.
Paul Johnston, spokesman for the U.S. Army Corps of Engineers, said the Missouri River is already between 3 feet and 7 feet above flood stage from Omaha, Nebraska, to its confluence with the Mississippi in St. Louis.
He said flooding is predicted in coming weeks for some cities downstream states, including the 8,000-population community of Nebraska City south of Omaha and St. Joseph, Mo., a city of 77,000 in the northwestern part of the state.
(Editing by Mary Wisniewski and Peter Bohan)