Of the three main parties vying for office in Ontario's spring election, only the NDP has spoken out against building a $2.4-billion nuclear waste bunker near Lake Huron.

NDP Leader Andrea Horwath said the idea of burying radioactive waste so close to a major fresh-water source worries her and, should she be elected on June 7, would look to intervene against the project.

"As a party, we're not in favour of having that facility in that location," Horwath said recently on the campaign trail. "It's something that we're quite concerned about. We know that other leaders, both in Canada and across the border in the States, have sent significant letters of concern and protest to the federal government in regard to the siting of this facility."

Ontario Power Generation argues the deep geologic repository at the Bruce Nuclear Generating Station near Kincardine, Ont., is by far the best and safest option for permanently storing the low- and intermediate-level toxic waste that has been stored for years above ground. The utility maintains the stable rock would ensure no radiation leakage for centuries.

However, scores of communities on both sides of the Canada-U.S. border have expressed alarm at the proposal. They maintain the consequences of contaminating the all-important fresh-water source is far too great to take.

"I hear big concerns from many different jurisdictions as well as individuals as well as communities," Horwath said. "As an individual, as an Ontarian, as a Canadian, I'm worried about it. It's problematic. I don't think it's smart to have any kind of nuclear storage on the edge of the lake."

The waste bunker, first proposed more than a decade ago, is currently awaiting final approval from the federal government. Ottawa has repeatedly stalled since an environmental review panel gave its approval three years ago.

Most recently, federal Environment Minister Catherine McKenna demanded the power utility come back with clear and unequivocal endorsement from affected First Nations, who have made it clear they are in no hurry to do that.

For her part, Liberal Leader Kathleen Wynne, who is vying for a second stint as premier, suggested the province has no role to play in the approval process.

"It's a federal issue," Wynne said. "They are dealing with municipalities, and we need to let that process roll out."

While Progressive Conservative Leader Doug Ford has not addressed the issue publicly, a party spokeswoman on the weekend was neutral on the wisdom of the proposal.

"The plan to bury low and intermediate nuclear waste must be done with local approval and in an environmentally sustainable way," Melissa Lantsman said.

At the same time, the Tories called nuclear power "critical" to Ontario.

"It's our cheapest, most reliable source of power and it powers more than 60 per cent of the province," Lantsman said.

The repository plan calls for hundreds of thousands of cubic metres of radioactive waste -- stored for years at the Bruce nuclear station site above ground -- would be buried 680 metres deep. OPG has warned the cost of the project could rise by billions if delayed significantly.

However, more than 100 mayors and other elected officials on both sides of the border -- they claim to speak for 16 million people -- urged McKenna in November to reject the proposed bunker. They noted that local, county and state governments representing 23 million people had passed 230 resolutions opposing the burial of nuclear waste anywhere in the Great Lakes basin.

Horwath agreed.

"When you're talking about water, and the fact that we can't live without clean water, we should be doing everything that we can not only to protect our fresh-water sources for our generation (but) for the next generations as well."