More than 60 homes in the Orchard Homes neighborhood of Missoula, Montana, have been ordered to evacuate as a river that flows through the city of 70,000 is expected to reach its second-highest level on record.

The Clark Fork River reached major flood stage on Thursday, and rain expected through Friday – combined with snowmelt from the higher elevations – will bring the river to its highest level since 1908 in the coming days. The expected flooding that occurs as the Clark Fork surges could last for days, according to river forecasts.

"The water locked in snowpack in the Upper Clark Fork River Basin remains 38 percent above average for the second week of May, according to NRCS SNOTEL estimates," said weather.com senior meteorologist Jon Erdman. "That remaining snowmelt, plus a chance of rain and a few thundershowers through Friday, will keep the Clark Fork River in Missoula well above flood stage into next week, if not beyond."

(MORE: The Latest Information on the Montana Floods)

Along the river, as many as 1,300 homes were warned to prepare for possible evacuations. NBC Montana reported that a state of emergency was declared on Monday for Ravalli County, south of Missoula, as flooding preparations continued.

"If you live anywhere near a stream or waterway in western Montana, you need to be prepared to leave your home," Missoula County Disaster and Emergency Services deputy coordinator Ken Parks said, as reported by the Associated Press. "This is going to come earlier than we expected. We're trying to get out ahead of this thing and get the message out that this could be a very dangerous situation."

The Missoula Sheriff's Office urged residents near the river or possible problem areas to evacuate, even if their home is outside the mandatory evacuation zone, according to KPAX.com.

The flooding poses another threat in Missoula and communities downstream. A nearby abandoned mill's old holding ponds could overflow, unleashing contaminants into the river, KPAX also said. Officials have worried about this possibility since before mill closed in 2010.

The Missoulian reported in February that the Environmental Protection Agency is assessing the risk of the Smurfit-Stone Mill ponds, which were used to cool water from the mill's operations, but Missoula County leaders have been pressing for cleanup and for more information.

A Missoula County Environmental Health Specialist told KPAX that the county has been watching the ponds' berms closely over the past few weeks and will continue to monitor them as the Clark Fork rises.