Recent heavy rains in western Manitoba and eastern Saskatchewan will produce flows along the Assiniboine River not seen since the 2011 flood.
Provincial officials were starting to notify landowners near the Portage Diversion and along the Assiniboine east of Portage la Prairie Wednesday to prepare for massive flows.
Some residents in the Headingley and St. François Xavier areas are being advised to sandbag their homes. An unknown amount of farmland in the area is expected to be flooded.
Flows along the Assiniboine will reach near 2011 levels.
Some 250 residents, mainly in southwestern Manitoba, have been displaced by flooding in recent days, bringing the 2014 total to 500.
41 municipalities and communities have declared states of emergency.
72 sections of provincial road have been closed or marked with a caution.
A rescue helicopter has been deployed in the Brandon area in case southwestern Manitoba families need to be rescued.
Some 17 streams in Manitoba including the Qu'Appelle and Vermilion rivers and Pipestone Creek are experiencing record flows.
Flood officials are now reassessing predicted peak levels for Lake Manitoba in light of the recent rains.
The Shellmouth reservoir in western Manitoba is full and overflowing.
Flows along the Winnipeg River are very high, and sandbags have been dispatched to the area. Lake St. Martin is at flood stage. Work began Wednesday to reopen an emergency channel constructed in 2011 to reduce lake levels.
The one saving grace is the forecast calls for at least five days of warm, dry weather.
-- source: Province of Manitoba
Assiniboine River levels in Brandon are anticipated to rise to near the 2011 peak in the coming days, although provincial officials say the city is well-protected.
"There's a major surge coming through the Assiniboine, and it's going to impact all the way throughout Manitoba... and right into Headingley and the city of Winnipeg," Infrastructure and Transportation Minister Steve Ashton said Wednesday.
Some 41 municipalities have declared states of emergency due to prolonged rains, exacerbated by big storms over the Canada Day weekend.
Many communities, especially in the southwestern corner of the province, have seen parts of roads and bridges inundated with water.
Ashton said the damage to municipal and provincial roads will be "significant," although it is still too early to estimate a cost.
The province said about 250 people were evacuated -- mainly in southwestern Manitoba -- in recent days, bringing the total displaced by flooding to 500 in 2014. Some 170 homes -- mainly in western Manitoba -- have recently been affected. Some have suffered basement flooding, while most have been isolated due to flooded roads leading to evacuations.
With a rush of water heading towards Winnipeg, the province has opened the Portage Diversion. On Wednesday, flows through the diversion, which channels water to Lake Manitoba, stood at 7,500 cubic feet per second.
Ashton did not rule out future flows of 25,000 cfs -- the diversion's original design capacity -- or more in the coming days. In 2011, flows through the diversion rose to 34,000 cfs.
"We're preparing it (the diversion) for a significant operation and that would include, obviously, the design capacity," Ashton told a news conference. "It could include some of the kind of levels we saw in 2011."
The big difference is the diversion is unlikely to operate at capacity for nearly as long as it did three years ago, the minister added.
Meanwhile, flood officials realize the Assiniboine River itself, east of Portage la Prairie, will have to carry much more water than it is now.
The province has regulated this section of the river recently so flows have not exceeded 10,500 cfs. At that level, farmland is largely unaffected by flooding, and homes are not at risk.
But with the recent storms, there is so much water coming from the west officials say they have no choice but to allow flows of 15,000 cfs or more in the coming days. (In 2011, after emergency fortifications, flows along the eastern section of the river peaked at 18,000 cfs.)
The province has started contacting vulnerable landowners and homeowners to take precautions. Residents don't have long to prepare themselves. Officials will start gradually increasing river flows east of Portage on Saturday.
Lee Spencer, head of Manitoba's Emergency Measures Organization, congratulated local municipal officials in southwestern Manitoba for responding quickly to the flood threat.
With many roads washed out or damaged, the province has deployed a helicopter in the Brandon area to rescue farmers and other residents who are threatened by floodwaters, he said.
-- with files from the Brandon Sun