The head of the Nuclear Regulatory Commission is headed to a Nebraska nuclear power plant where floodwaters breached a levee and forced engineers to switch to backup power.

Water from the swollen Missouri River surged through a levee protecting the electrical power supply at Nebraska's Fort Calhoun Nuclear Station on Sunday, reaching containment buildings and causing engineers to activate backup generators. The plant was closed in April for refueling and remained closed because of flood warnings.

Nuclear Regulatory Commission Chairman Gregory Jaczko will fly over the plant Monday and then meet with officials to discuss the problem. Jaczko said safeguards against natural disasters were built into the plant.

Mother nature takes care of the floods, so we have to do the best we can to make sure we're prepared, and all the plants in the U.S. have been designed to deal with historically the largest possible floods, Jaczsko said.

However, ABC reported that some watchdog groups remain skeptical, pointing to safety violations workers incurred for failing to maintain procedures for combating a significant flood. A recent Associated Press analysis revealed widespread lapses in the regulation of U.S. nuclear sites, finding that regulators often rewrote rules or manipulated data to conceal violations at aging plants.

Record floods have engulfed communities in states from Montana to Iowa. In Minot, North Dakota flooding from the Souris River has forced residents to evacuate their homes and threatened another nuclear site - silos containing Minuteman III nuclear missiles.