The governor of flood-plagued Montana ordered more National Guard troops to join the anti-flood effort, while states downstream along the bloated Missouri River strengthened levees and laid sandbags ahead of the release of waters from dams and reservoirs.
More rain fell Sunday on soaked Montana communities after more than a week of floods in the region, with the National Weather Service predicting up to 3 inches before it tapers off Monday. Previous storms brought as much as 8 inches to some areas of the state.
For the second straight weekend, forecasters blanketed much of the central and eastern regions of Montana with flood warnings.
Gov. Brian Schweitzer Sunday sent 36 National Guard soldiers to Roundup, a town northwest of Billings in central Montana that remained inundated by several feet of water for a fourth day.
Only one road leading into the agriculture and mining town was open, and the governor's order to deploy the National Guard to the community came a day after he sent 50 guardsmen to the Crow Reservation, which also has been inundated by heavy flooding.
The National Guard contingents were to provide unarmed security checkpoints.
Officials warned ongoing flooding could ultimately be the worst in decades for the state, with an unusually heavy snowpack in the mountains, persistent spring rains and waterlogged ground incapable of soaking up any more moisture.
"No part of the state" will escape some type of flooding, Monique Lay, spokeswoman for the state Emergency Coordination Center, said in anticipation of more rain and melting snowpack. "It's statewide, corner to corner."
Downstream, about 1,500 North Dakota National Guard soldiers were summoned to help in the flood effort as residents in Bismarck, N.D., and nearby Mandan brace for large volumes of water to be released in the coming weeks at Garrison Dam.
But the U.S. Army Corps of Engineers' said construction of more than seven miles of earthen levees to protect against flooding in Bismarck and Mandan should be completed long before planned maximum releases at Garrison.
The river is burgeoning with the runoff of rain and melting snow in Montana, Wyoming and western North Dakota.
South Dakota Gov. Dennis Daugaard said Sunday that the Corps' decision to release even more water from Missouri dams will not only cause additional problems for the central South Dakota communities of Pierre and Fort Pierre, but also for the downstream cities of Yankton and Dakota Dunes in the state's southeastern corner.
Hundreds of homeowners in Pierre and Fort Pierre also have been working feverishly for several days, moving their belongings to higher ground and laying sandbags around the houses. Water had already moved into some residential areas.
Meanwhile, officials in Nebraska and Iowa have been monitoring the river, which is expected to crest near Omaha at record levels between 30 and 35 feet in late June after more water is released from reservoirs.
In perhaps a sign of weariness in Montana, the state Emergency Coordination Center on Sunday felt compelled to issue a statement saying Fort Peck Dam is not in danger of failing in an effort to quell what spokeswoman Lay said were persistent rumors being voiced at many local meetings.
"There is a lot of frustration and devastation," said Lay about what residents are facing.
The spillway at Fort Peck Dam, which backs up the 134-mile long Fort Peck Lake, operated earlier this month for the first time since 1997, said Jody Farhat, Chief of the Missouri River Basin Water Management office with the U.S. Corps of Engineers.
She said water will pass over the spillway again starting Thursday as the Corps plans to build to a record release of 50,000 cubic feet per second by June 6. The previous record, she said, was 35,000 cfs in 1975. She reiterated that the dam is absolutely safe.
Farhat said all six mainstem dams on the Missouri River are being operated in a coordinated way to handle what she said is likely a record runoff for the basin.
Associated Press writers Chet Brokaw in Pierre, S.D., and James MacPherson in Bismarck, N.D., contributed to this report.