The Canadian Nuclear Safety Commission is assessing a leak that occurred at the Point Lepreau nuclear generating station in New Brunswick over the weekend.
Water laced with low levels of the toxic chemical hydrazine spilled into the Bay of Fundy on Sunday.
NB Power informed the Canadian Nuclear Safety Commission (CNSC) about the spill on Monday.
The leak of the non-radioactive product has since been isolated and contained, the CNSC said in a statement.
Water samples taken on the beach near the plant show the hydrazine levels are now below detection, it said.
CNSC is assessing the incident and the measures taken by NB Power to prevent a recurrence.
The "event" will also be discussed at an upcoming public commission meeting, the statement said.
Hydrazine is used to strip oxygen from water in steam generators. It protects the generators from corrosion and maintains the proper water chemistry.
The "light water" leaked from a valve on the non-nuclear side of the plant, officials said.
Two years ago, 23 barrels of water mixed with the chemical leaked into the Bay of Fundy.
Three weeks later, there was a radioactive spill in the plant when six litres of heavy water splashed to the floor.
At the time, the head of Canada's Nuclear Safety Commission called the events “unsettling.”
Point Lepreau is Atlantic Canada's only nuclear reactor.