WINNIPEG -- A new report says the province miscalculated flood protection estimates in the Interlake outlet channels design.

The $540 million plan would see water flow from Lake Manitoba to Lake Winnipeg via Lake St. Martin.

The flood mitigation project has been in the works since the devastation caused by the 2011 flood.

Area First Nations commissioned a report by Halket Environmental Consultants to study the project’s potential impact on Lake St. Martin.

It concluded a channel of water known as The Narrows acts as a bottleneck creating higher flood water levels in the lake’s south basin. The report said this was not accounted for in a 2013 environmental assessment.

“This finding casts doubt on the level of protection offered by the outlet channels for a 2011 flood event,” the report said.

The report’s author Ian Halket said the project could cause flooding in the south basin.

“The levels that Manitoba has predicted in terms of flood mitigation are overestimated,” said Halket

The Interlake Reserves Tribal Council represents the area communities. Its chair, Lake Manitoba First Nation Chief Cornell McLean, said they have concerns about how the project could damage the lake’s surroundings.

“Whether they’re using it for a reservoir, a flow through. It ain't going to work," said McLean. "The First Nations around that area are going to be impacted by the waters again.”

The province said it’s well aware of the issue. It commissioned its own report, completed three weeks ago. Manitoba Infrastructure Minister Ron Schuler said he is confident design changes, in the works, will solve the problem.

“We’re designing it for a 2011 flood event so that’s the benchmark,” said Schuler.

McLean said he was unaware the province studied The Narrows.

“I haven’t seen that report, you know it’s probably going to come in the mail next week,” he said.