Infrastructure Minister Steve Ashton said the channel could be completed by 2020 at a cost of up to $450 million, including modifications to the current emergency channel at Lake St. Martin.
The province has narrowed the project down to two options and is starting consultations.
"It's a very significant investment," Ashton said Thursday. "But it's not only the right thing to do, it's the only thing to do."
This summer Manitoba struggled as flood water poured in from Saskatchewan, prompting the province to declare a state of emergency and call on the military to help with frantic sandbagging efforts.
Flood water is diverted away from Winnipeg primarily through the Portage Diversion channel, which ends up pushing water levels up in Lake Manitoba or Lake Winnipeg.
The government quickly constructed a $100-million emergency channel at Lake St. Martin after a flood in 2011, but promised in July that it would do more to ease pressure on Lake Manitoba.
Residents around Lake Manitoba who have suffered chronic flooding slammed the province for taking seven years to offer relief. But Ashton said there are 31 steps the government has to take before it even starts construction on the channel.
"This is 2014. In the year 2014, you can't do maybe the way you did it 50 or 60 years ago," Ashton said. "You can't ignore environmental concerns and, in particular, you can't ignore First Nations."
Progressive Conservative critic Shannon Martin said the steps laid out by the government assume the province is incapable of doing things simultaneously. The government also lists issuing a news release as one of the steps, he noted.
If the province was serious about preventing flooding, it would open the existing emergency channel to full capacity, he said.
The Tories say aerial photos shot by a local resident show the channel at Lake St. Martin is partially blocked.
"Almost three months ago the NDP warned Manitobans of dire consequences if the Lake St. Martin channel was not open," Martin said. "They say a picture is worth a thousand words. It can be summed up in three — it's not open."
But Ashton said the channel is operating at about 75 per cent capacity. It doesn't matter what the opening looks like but how much water is actually flowing through the channel, he said.
The channel has already brought Lake St. Martin down to below flood levels, Ashton said.
"It's not the width of the channel, it's the flow of the water," he said.
"You can take all the pictures you want. The only thing that matters is how much water you're flowing and how much it brings the level of the lake down."