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Park Service managers at Lake Mead contend they’ve done more than anybody to try to keep mussels from leaving, but cite privacy laws governing boaters’ personal information they say prevent them from passing along details from boaters to states.

Randy Lavasseur, assistant chief ranger at the Lake Mead National Recreation Area, said the vastness of the 248-square-mile reservoir, where water behind the Hoover Dam is diverted through pipelines and aqueducts for use in California, Arizona and Nevada, presents a challenge to federal managers in making sure every boat that leaves is mollusk-free. More than 8 million people visit every year.

Other states also are casting a wary glance at Lake Mead.

At sparkling Lake Tahoe on the California-Nevada border, two infested boats were intercepted before the July 4 holiday.

Both came from Lake Mead, said Ted Thayer, who manages the Tahoe Regional Planning Agency’s aquatic invasive species program. His group estimates damage from a mussel-infested Lake Tahoe would result in $22 million in annual costs to the water supply, recreation and property values.

“We’re concerned they are still showing up here,” Thayer said from his offices in Stateline, Nev. “One really infested boat would be enough to infest” Lake Tahoe.

So far, managers at Glen Canyon National Recreation Area on Lake Powell in Arizona and Utah believe a mandatory inspection program has helped keep their waters mussel-free. Boaters who fail to abide by inspection rules face a mandatory court appearance, six months in jail and a $5,000 fine.