The release happened Sunday when light water leaked from a valve on the non-nuclear side of the Point Lepreau Generating Station, according to the company. The release is contained, it said.
NB Power said samples taken Sunday along the shoreline of the Bay of Fundy contained 0.009 parts per million of hydrazine.
In a statement, the company said the concentration is "less than federally recommended guidelines that determine impacts on marine life or ecological systems." Testing Monday found levels below detection, the company said.
"NB Power will continue to monitor the area and take additional samples,” Claire Harris, a manager at the generating station, said in an statement.
“Following a thorough investigation, NB Power will determine the appropriate measures to implement and prevent recurrence.”
Hydrazine is used to strip oxygen from water in steam generators. It protects the generators from corrosion and keeps the proper water chemistry.
It’s not the first time hydrazine from Point Lepreau has been released. 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.”