A group of mayors from communities on both sides of the Canada-U.S. border is calling for the rejection of a Wisconsin city's precedent-setting request to draw water from the Great Lakes.

The Great Lakes and St. Lawrence Cities Initiative spoke out on Thursday, ahead of a meeting in the U.S. next week where a decision is expected on the water diversion application from the city of Waukesha.

The group is urging the governors of eight Great Lake states -- who will have the final word on the issue -- to reject Waukesha's request, saying the application violates a regional agreement, sets a dangerous example and has been through a flawed consultation process.

"If this starts to spread, how far is it going to spread? And it's going to continue to spread," said Randy Hope, the mayor of Chatham-Kent municipality in southwestern Ontario, who is on the group's board of directors.

"We live in those communities, we understand those communities, we work with the ecosystems, we're doing our best to clean up the Great Lakes Basin and what we have is people saying 'well, I want some of that."'

Waukesha, a city of about 70,000 people, wants to divert water from Lake Michigan because its own aquifer is running low and the water is contaminated with high levels of naturally occurring cancer-causing radium.

Under a current regional agreement between eight U.S. states and Ontario and Quebec, diversions of water away from the Great Lakes-St. Lawrence River basin are banned, with limited exceptions that can be made only when certain conditions are met.

Waukesha wants to become the first such exception, arguing that although it's located outside the boundary of the Great Lakes basin, it is part of a county straddling that geographical line. It also promises to return treated water to Lake Michigan.

Canadian and American opponents of Waukesha's plan have warned the city's request, if approved, could set a risky precedent for other communities facing water shortages.

But last month, the city's request received preliminary approval from representatives of the Great Lake states, Ontario and Quebec who said Waukesha's application would comply with the regional agreement if certain conditions were met.

Those conditions include service to a smaller area and an average limit of 31 million litres a day.

But the mayors from the Great Lakes and St. Lawrence Cities Initiative say the amended service area is still too large, the return flow of water to Lake Michigan through the Root River has not been analysed closely enough, and the approval process dealing with Waukesha's request has not allowed enough public participation.

"This is drawing from a community resource, and the community resource is the Great Lakes Basin," Hope said, who argued that Great Lake communities weren't adequately consulted. "We have to speak up and let our voices be heard."

The group has suggested Waukesha treat the radium in its groundwater supply instead of taking water from Lake Michigan.

It also believes other cities are closely watching Waukesha's case and are ready with their own requests to divert water from the Great Lakes if the city succeeds.

"We expect there to be a series of applications and all of those can and will have an impact on our Great Lakes," said John Dicker, mayor of Racine, Wis., through which the Root River that would carry Waukesha's return flow runs through.

"We are here as 120 plus mayors to protect our Great Lakes."

Waukesha's application needs a unanimous vote of approval by eight states to get the final green light. Ontario and Quebec do not get a vote but they have submitted their views and recommendations on the issue.

Ontario had previously expressed concerns about Waukesha's request and found that the potential impacts of the proposed diversion on Great Lakes water quantity had not been sufficiently assessed.

Its review of the matter also acknowledged that Waukesha's proposal was likely just the beginning of similar requests.

The Great Lakes support 33 million people, including nine million Canadians and eight of Canada's 20 largest cities, according to the federal government.