I’m standing at one of the big locks in Massena as a tanker the size of a city block squeezes through the massive gates. Water pumps in and lifts the ship so it can continue on its way toward Lake Ontario. This tanker is carrying hazardous materials, a kind of heavy petroleum, so visitors like me are shooed away to a safe distance. "At this point we have to ask everyone to come down from the observation deck," the loudspeaker announces. "As a reminder, there is no smoking allowed."

Freighters passing through the St. Lawrence Seaway make dozens of precision maneuvers just like this one, passing through narrow locks and channels and navigating among hordes of pleasure boats. Last year a debate began over whether the route is safe enough for the shipping of nuclear waste.

"When will the McGuinty government finally stop passing the buck and order [Ontario Power Generation Inc.] to slam the breaks on this harebrained to ship radioactive nuclear waste through the Great Lakes?" asked Andrea Horvath, leader of the New Democratic Party in Ontario.

Speaking last September, Horvath blasted a plan by a company called Bruce Power to use the Seaway to transport old nuclear reactor parts to Europe for reprocessing.

"Seventy Great Lakes mayors, dozens of environmental groups and first nation groups all oppose shipping sixteen radioactive nuclear steam generators through the Great Lakes to Sweden," Horvath said.

The Mohawk community, whose reservation straddles the St. Lawrence River, raised the fiercest objections.

Nuclear power generates more than half of Ontario’s electricity and many Canadians supported the idea. "This process that they’re undertaking will allow Bruce to reduce the volume of waste that they have in storage by about 90%, Mr. Speaker. That’s a pretty good contribution in terms of improving environmental circumstances here in this province and across the country." said Brad Duguid, a Liberal Party leader and Ontario’s Energy Minister.

In February, Canada’s Nuclear Safety Commission approved the shipments, saying that the project could be done safely and arguing that there is negligible risk to people or the environment along the river. This spring the US Department of Transportation announced that it had begun a separate review of the plan.

Meanwhile, the scrutiny and criticism have caused Bruce Power to delay plans for the nuclear shipment, withdrawing their application to the US Department of Transportation. According to a spokesman for the company, they hope to hold talks with native groups in Canada that are still opposed to the shipments.

Jennifer Caddick with a group called Save the River pilots her boat through one of the narrowest channels of the Seaway near Clayton. Houses and farms sit just a few hundred yards from the main shipping lane. Caddick says the nuclear shipment debate took people here by surprise. "The only way communities on the US side found out about that proposal was through media reports," Caddick said.

Caddick said she thinks the shipments are a terrible idea. In the months since they found out about the Bruce Power project Caddick says her group has begun demanding more information about other kinds of hazardous materials that are already passing through the Seaway.

"So it made us question and ask what else is being transported through here that we don’t know about it? You know, what other chemicals, or other items that could be hazardous if there’s an accident. We just went through that super narrow part of the river. Accidents happen, several a year."

Caddick says they're still waiting for detailed information about shipments.