Courtesy NRC

WASHINGTON (AP) — The nation’s oldest nuclear power plant is on alert after waters from a colossal storm reached high levels.

Oyster Creek in Lacey Township, N.J., was already offline for regular maintenance before Sandy, a superstorm downgraded Monday night from a hurricane, slammed the East Coast.

The Nuclear Regulatory Commission says an “unusual event” was declared around 7 p.m. when water reached a high level. The situation was upgraded less than two hours later to an “alert,” the second-lowest in a four-tiered warning system.

Federal officials say all nuclear plants are still in safe condition. They say water levels near Oyster Creek, which is along the Atlantic Ocean, will likely recede within a few hours.

Oyster Creek went online in 1969 and provides 9 percent of New Jersey’s electricity.