NORTH PERRY, Ohio—A water system problem caused an automatic shutdown of a nuclear power plant yesterday, a spokeswoman for the plant said.

The Perry Nuclear Power Plant, located alongside Lake Erie about 35 miles northeast of Cleveland, shut down about 7:30 a.m. when problems with the system that provides water to the reactor malfunctioned, said spokeswoman Jennifer Young.

Water level inside the reactor was adequately maintained, but the plant remained off-line late last night. A special inspection team from the U.S. Nuclear Regulatory Commission will try to determine what caused the problem, Young said.

"Nuclear plants in general do shut down from time to time, but we have not seen this particular problem before," Young said.

The plant, owned by Akron-based FirstEnergy Corp., is safe and stable, she said.

Workers shut down the plant last December because of a fluctuation in the water system. However, an investigation later determined that the problem was caused by a leak in a system that runs air-operated valves.

The Nuclear Regulatory Commission, after conducting a special review of the plant, said in 2005 that it rated the plant safe but noted a string of problems and said it would continue heightened supervision.