David Heurtel said the central Quebec region of Mauricie is expected to bear the brunt of the precipitation.
"We're looking at considerable rainfall on the weekend," he told a news conference.
"Depending on the region, we're talking about 20 to 40 millimetres but in Mauricie the impact will be even greater, so we should expect another tough weekend there."
Residents in a canoe paddle on the flooded streets in Pierrefonds on Sunday. (Photo: Catherine Legault/AFP/Getty)
Heurtel said the combination of rain, melting snow in the St-Maurice River basin and rising tides could prove to be damaging in the region.
Trois-Rivieres resident Patrice Bourassa, who has been co-ordinating volunteer efforts in Mauricie, said citizens in some of the worst-hit regions are losing energy and patience.
"It's reached the point they have to leave their homes in the morning and take a canoe to their vehicle 500 metres away because it's too flooded," he said in a telephone interview.
A man makes his way through the flooded streets in Laval, Que., on Wednesday. (Photo: Ryan Remiorz/CP)
Bourassa said the Facebook page he created has already drawn 1,200 members, with many spending the last few days building dikes, packing sandbags and helping citizens.
He says that while city officials have offered all the help they can, some of the smaller towns in the region have fewer resources to deal with flooding.
The mayor of Nicolet, Que. said the small town at the confluence of the St. Lawrence and Nicolet rivers had put out a voluntary evacuation order in advance of the rising waters.
A flood victim looks through donated clothes at the local community centre in Deux-Montagnes, Que., on Wednesday. (Photo: Ryan Remiorz/CP)
Genevieve Dubois fears the water levels could rise by 25 centimetres putting up to 300 homes at risk and cutting off road access to the town.
But she said most people were staying put and planned to simply monitor the water level after a major sandbagging effort she hopes will keep most houses dry.
"People are starting to get tired but the morale is still there," she said.
Levels expected to remain stable in Montreal
Levels are expected to remain stable in flooded areas in the Greater Montreal area, where Heurtel credited the management of water flow from the Ottawa River and Great Lakes basins with preventing the situation from getting worse.
Weekend rain isn't expected to cause a spike in Montreal-area water levels, Heurtel said.
"The flow will continue decreasing and ultimately the rains that are going to come are going to slow down the decrease," Heurtel said.
"We're not looking at the rainfall rising the levels. It's going to slow down the decrease or it's going to be maintained at the same levels."
Flood waters breach the Gatineau River and flood the neighbourhood on Wednesday in Gatineau. (Photo: Sean Kilpatrick/CP)
Meanwhile, Public Security Minister Martin Coiteux told the same news conference that 3,882 residences in the province have now been affected by the floods.
Coiteux also said 2,721 people have had to leave their homes and that there have been 126 landslides.
In Ottawa, Defence Minister Harjit Sajjan said the military is deploying several hundred more Canadian soldiers to help with flood relief efforts in Quebec, bringing the total to 2,200 by the end of the day.
A military vehicle drives along a flooded street on Wendesday in Gaitineau, Que. (Photo: Sean Kilpatrick/CP)
Sajjan said about 470 army reservists from Ontario had started arriving in Quebec to fill sandbags, evacuate people and provide other assistance.
In Montreal, fire Chief Bruno Lachance said the focus is on consolidating dams and that he doesn't expect the number of evacuees to rise.
State of emergency still in effect
A state of emergency remains in effect in Montreal until Sunday, with Lachance saying 243 people have been evacuated and about 400 homes flooded in the city.
"We know it will take days before it recedes totally — maybe weeks," he said. "We ask people to be patient, we're going to help them when the time comes, (but) for the moment, we're still in an emergency situation."
At least one person has died in the province because of the floods — a man whose car ended up in a surging river in the eastern Gaspe region on Sunday.
Authorities resumed their search Wednesday for a two-year-old girl who disappeared in the same incident but put it on hold later in the day. It will pick up again Thursday with additional provincial police officers who are specialized in searches in water and on riverbanks.
The Canadian Red Cross has set up a relief fund, with the federal government contributing $1 million and the Quebec government $500,000.
Other Quebec municipalities have also contributed, notably Montreal, which has pledged $250,000.
— with files from Morgan Lowrie in Montreal.
Also on HuffPost