WINNIPEG -- A report commissioned by Manitoba warns flood protection in the province has dozens of significant weaknesses and needs $1 billion in upgrades now to prevent billions in damage down the road.

The 1,600-page study details more than 100 vulnerabilities.

It says defences along the Assiniboine River between Portage la Prairie and Winnipeg are particularly weak and suggests that a flood in the area has the potential to cause up to $2 billion in damage if they fail.

In 2014, Manitoba had to declare a state of emergency and ask the military for sandbagging help when floodwater poured into the Assiniboine River watershed from Saskatchewan.

The province was also battered by one of the worst floods in its history in 2011. Army reservists scrambled to help shore up weakened dikes and sandbag homes along the Assiniboine River.

"The flood of 2011 highlighted several potential weak links in the existing flood-control systems. The shortcomings of the system were emphasized again in 2014," says the study by engineering firm KGS Group.

The Portage diversion -- a channel that moves water from the river to Lake Manitoba -- needs $373 million in upgrades alone, the report says. The diversion has been pushed to over-capacity in recent years and risks mechanical failure, it says. Without upgrades, there is a "potential inability to operate the control structure."

The report says dikes along the riverbank also need "urgent attention and upgrading" worth $273 million.

The province's emergency preparedness is also vulnerable, the study suggests. An unprecedented flood might require mass evacuations, including from the city of Winnipeg, and officials need to prepare for a dike breach or electrical failure which could affect flood-control structures.

"Evacuation on a large scale has not been planned and execution would be fraught with difficulties without prior planning," the report says.

"It may be that such an extreme flood might not occur in southern Manitoba for many years. By that time, many of the engineers/planners/officials who currently have the first-hand knowledge provided by direct experience will no longer be available."

Premier Greg Selinger said the upgrades have been on the government's radar for a while and are a necessary investment.

"A community under water has no economy, so we have to move forward," he said Wednesday. "We've always known that we're going to have a very significant investment required to protect these communities."

The NDP raised Manitoba's provincial sales tax to eight from seven per cent in 2013, arguing the increase was necessary to pay for needed infrastructure. Selinger, who faces a provincial election in April, said the report shows why that spending is crucial.

"We need to do it now because you never know when that next major flood could occur."

People who live along the Assiniboine River are skeptical.

Dwayne Clark, reeve of the Rural Municipality of St. Francois Xavier, said spending millions raising dikes and building up people's homes won't lessen the impact on residents and the local economy.

"People are less inclined to build their business in a zone that is prone to flooding, whether there is flood protection there or not," Clark said. "No one is going to be building a tourist attraction with a big ring dike around it."

Opposition Conservative Reg Helwer said the government has ignored flood infrastructure along the Assiniboine River for years. Now, he said, it's paying the price.

"There are critical hotspots that need to be addressed," said Helwer. "Those are areas we would look at investing in once we've figured out where this government has spent all the money."