The Palisades nuclear plant in Michigan shut down early Sunday morning when water leaking from a tank passed a threshold set earlier by federal regulators.

The leak from the safety injection refueling water tank had increased to 90 gallons per day before the manual shutdown, according to an event report filed with the Nuclear Regulatory Commission, exceeding a 34 gallon limit. At that point, the report indicated plant workers had not found the source of the leak or the cause of its increase.

An NRC spokeswoman told the Kalamazoo Gazette that the plant released about 79 gallons of radioactive water into Lake Michigan, although it was highly diluted and did not present a risk to public health. The paper noted the tank was also the source of a leak that seeped into the control room and caused a shutdown last year – one of four in 2012.

Entergy owns the plant near South Haven, Mich., which uses a single Combustion Engineering pressurized water reactor first licensed in 1971, according to the NRC.