RENO, Nev. (AP) - Lake Tahoe's economy could lose millions in taxes and tourism revenue if invasive mussels become established in the lake's famed blue waters, according to a new report.

The report prepared by the U.S. Army Corps of Engineers estimated that the Tahoe economy could suffer an annual loss of $22 million because of lost tourism, declining property values and maintenance costs associated with the mollusks, according to a Reno Gazette-Journal story published Wednesday.

"This is just so frightening," said Allen Biaggi, director of the Nevada Department of Conservation and Natural Resources and chairman of Tahoe Regional Planning Agency's policy board. The agency was scheduled to discuss the report's findings this week.

Quagga mussels first turned up in Lake Mead in early 2007 and have spread to other waters in southern Nevada and California. Zebra mussels were discovered in a reservoir about 250 miles from Tahoe in January 2008.

The mussels have wildlife officials around the country on alert because once they become entrenched, they multiple quickly and there's no way to get rid of them.

Experts said that if the mollusks establish themselves, they could forever alter Lake Tahoe's sensitive ecosystem, clog water intakes, encrust boats and docks and cover now-pristine beaches with sharp, smelly shells. Biaggi also said they could eventually spread down the Truckee River to Pyramid Lake north of Reno.

Lake Tahoe regulators instituted boat inspections for the mussels last summer, including mandatory checks for vessels from other areas. When boats exit the lake, a seal is fixed between the boat and trailer. If the seal is intact when the boat launches again, no new inspection is required.

Regulators imposed a fee-based program this June to ensure that inspections continue. Over the Memorial Day weekend, inspectors decontaminated six boats for invasive mussels.

Biaggi said stopping the mollusks is the agency's second priority for protecting the lake that straddles the Nevada-California line, topped only by the prevention of catastrophic wildfires.

"Anytime you get something that can't be undone, that rises to a higher level," said Phil Brozek, senior project manager for the Army Corps of Engineers. "I've heard people say it's the most important issue, maybe because it's irreparable."

In addition to the invasive mollusks, the Army Corps report also said at least 20 nonnative species have established in the Lake Tahoe region. Ted Thayer, the agency's natural resource and science team leader, said there was also concern that Asian clams, more common in the lake than previously thought, could discharge calcium that in turn could encourage establishment of the quagga and zebra mussels.

Often, one species can facilitate another" by creating an environment favorable to other nonnative plants or fish that then
compete with native species, Thayer said.

Controlling their spread and preventing the introduction of other invasive species are necessary to keep the lake's ecology in balance, he said.