On March 14, 2011, Ontario Power Generation has notified Canada's federal nuclear regulator about the release of 73,000 litres of demineralized water into Lake Ontario at the Pickering A nuclear generating station.
The leak occurred at the plant located about 35 kilometres east of Toronto and was caused by a pump seal failure.
"The radiological risk to the environment and people's health is negligible," the Canadian Nuclear Safety Commission said in a statement.
The nuclear regulator and Environment Canada are monitoring the situation, the statement said.
Andrew Nichols of CBC News reported about the leak on Wednesday afternoon and said he spoke to an Ontario Power Generation spokesperson who told him the risk is minimal but that such leaks are not supposed to occur.
Nichols also spoke to Gordon Edwards of the Canadian Coalition of Nuclear Responsibility.
"In his words, 'What the hell is considered negligible?'" Nichols reported. "[Edwards] is concerned that it's the nuclear industry that is telling you and I and telling the public what is considered to be negligible but he's concerned that we don't have a proper sense of what negligible is," reported Nichols.
Nichols also reported that the leak could be a concern because Lake Ontario is the main source of drinking water for millions of people who live along the lake.
The leak comes as the world is watching Japan's unfolding nuclear crisis, as multiple reactors face cooling system failures and possible meltdowns in the wake of Friday's earthquake and tsunami.
Pickering A is the first of four reactors at the nuclear plant just east of Toronto. It went into service in 1971 and continued to operate safely until 1997, when it was placed in voluntary lay-up as part of what was then Ontario Hydro's nuclear improvement program.