A water-filled berm protecting a nuclear power plant in Nebraska from rising floodwaters collapsed Sunday, according to a spokesman, who said the plant remains secure.
Some sort of machinery came in contact with the berm, puncturing it and causing the berm to deflate, said Mike Jones, a spokesman for the Omaha Public Power District (OPPD), which owns the Fort Calhoun plant.
The plant, located about 20 miles north of Omaha, has been shut since April for refueling.
"The plant is still protected. This was an additional, a secondary, level of protection that we had put up," Jones said. "The plant remains protected to the level it would have been if the aqua berm had not been added."
Parts of the grounds are already under water as the swollen Missouri River overflows its banks, including areas around some auxiliary buildings, Jones said.
In addition to the berm, authorities have put in place flood gates and other barriers to help protect the facility.
The plant is designed to withstand waters up to 1,014 feet above mean sea level, according to the OPPD. The river currently stands at 1,006.3 feet and is not expected to exceed 1,008 feet, the Power District said.
Heavy rainfall in Montana and North Dakota, combined with melting snow from the Rocky Mountains, have sent the Missouri surging downstream this summer. The river washed over and punched through levees in nearby northwestern Missouri, spurring authorities to urge about 250 nearby residents to leave their homes.
The 6 to 12 inches of rainfall in the upper Missouri basin in the past few weeks is nearly a normal year's worth, and runoff from the mountain snowpack is 140% of normal, according to forecasters.
CNN's Patrick Oppmann contributed to this report.