Montana's Clark Fork River reached major flood stage Thursday, threatening additional homes.
The National Weather Service expects it to rise to a 100 year mark by this weekend and stay at major flood level for at least a week.
The Clark Fork surged past 13 feet and is on track to crest Saturday at 14 feet near Missoula.
Search and rescue teams evacuated people from a tent surrounded by water.
Authorities had previously ordered about 60 homes to evacuate, but now about 820 homes were under an evacuation warning.
The river is expected to say at major flood level for at least a week. At major flood stage, between 800 and 13-hundred homes in low-lying areas across missoula could be threatened.
A group of volunteers spent the day stacking sandbags and trying to prevent more flood damage.
On a Missoula bison ranch, flood waters have overtaken about half of the land where the bison roam and graze.
The bison still have some high ground that they can get to, but no one knows yet, how far up the water will flow.
Nearly all of the water is coming from the rapidly melting snowpack in the mountains around Missoula.
Near-record snowfall over the winter has caused flooding this spring across western Montana and central Montana.
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