More than 100 mayors and other elected officials on both sides of the Canada-U.S. border are urging Environment Minister Catherine McKenna to put the kibosh on a proposed nuclear-waste bunker near Lake Huron.

In an open letter to McKenna on Thursday, the officials say they speak for 16 million people who want the Ontario Power Generation proposal shelved as a potential eco hazard.

"We are deeply concerned that Ontario Power Generation (OPG) is proposing to bury nuclear waste in close proximity to the Great Lakes," the letter states. "We find it irresponsible and deeply troubling that OPG failed, and continues to refuse, to investigate any other actual sites."

The 104 signatories include mayors, wardens and reeves in Ontario, among them Keith Hobbs, of Thunder Bay, Maureen Cole, of South Huron, Heather Jackson, of St. Thomas, and Pat Darte, from Niagara-on-the-Lake. American signatories include mayors Ron Meer, of Michigan City, Ind., Stephen Hagerty of Evanston, Ill., and Mike Vandersteen, of Sheboygan, Wisc.

A covering note from Mayor Mike Bradley of Sarnia, Ont., says the message in the letter is clear.

"We oppose the risk to our precious fresh water," Bradley writes.

The Ontario Power Generation project, estimated to cost $2.4 billion and growing, would see a bunker built at the Bruce nuclear power plant near Kincardine, Ont., close to the Lake Huron shoreline. Hundreds of thousands of cubic metres of low and intermediate radioactive waste -- stored for years at the site above ground -- would be buried 680 metres deep.

The proposed storage, which OPG argues is the safest and most effective way to deal with the waste, won tentative approval from an environmental review panel in May 2015. Since then, both the previous Conservative and current Liberal governments have repeatedly delayed making the politically fraught final decision and OPG has warned the cost of the project could rise by billions if delayed significantly.

Earlier this year, OPG offered more information at McKenna's request on alternative sites -- although critics decried the analysis. In August, the minister asked for more information on the impact of the proposed bunker on the area's Indigenous people whose support is critical as to whether the project proceeds.

The Saugeen Ojibway Nation said last week that they are deliberating -- a process likely to take at least a year to play out. If they approve, the federal government will make a final decision on whether to allow OPG to proceed and under what conditions -- but the critics want an end to the process now.

The letter to McKenna takes issue with an OPG assertion that people are generally untroubled by the idea of burying waste that remains radioactive for centuries near Lake Huron.

It notes that local, county and state governments representing 23 million people have passed 230 resolutions in opposition to burying nuclear waste anywhere in the Great Lakes basin.

"We the undersigned request that you act to protect North America's most precious resource and the health and safety of the millions of people who rely on your leadership by rejecting OPG's application," the letter says.