Lake Tahoe is under siege by clams the size of your thumbnail.
The population of the coffee-colored Asian clams has soared in the southeast portion of the lake, threatening to hog food sources and excrete nutrients that foster algae growth, according to an annual Lake Tahoe report by UC Davis researchers.
Scientists worry that calcium in the clams' shells could make the lake more hospitable to invasion by quagga or zebra mussels, which cluster onto boats and anything else that rests in the water. Although the mussels have not been sighted at Tahoe, authorities at other lakes have spent millions of dollars trying to control them.
"In a lake like Tahoe where a lot money and a lot of effort is being put into maintaining its pristine nature, the introduction or the threat of invasive species really pulls us away from that pristine condition," said John Reuter, associate director of UC Davis' Tahoe Environmental Research Center, which released Tuesday's "Tahoe: State of the Lake Report."
No one is certain how the Asian clam first arrived at Lake Tahoe, whose famed clear waters lie at the center of a multimillion-dollar tourism economy. Some authorities say that fishermen used the clams as bait and that surviving clams took root on the lake's bottom, where they released tiny offspring that were carried by water currents to other parts of the lake.
Visitors first noticed the white, partially oxidized shells on the shore seven years ago.
"We've been aware of the Asian clam problem in Tahoe since 2002, and it's been just the past couple of years that it appears these clams have proliferated fairly rapidly," said Dennis Oliver, a spokesman for the Tahoe Regional Planning Agency, a bi-state agency that has spent more than $1 billion in federal, state, local and private money on restoration efforts at the lake.
Investigations are underway to determine whether the clams have moved from southeast areas such as Marla Bay to other parts of the lake. A small population has been found near Emerald Bay, along the southwest shore.
Authorities are testing removal methods such as suctioning out the clams and covering their beds in plastic to smother them. Environmentalists have called for increased inspections of boats to make sure quagga and zebra mussels don't get in.
"We think the time has come for additional measures to protect the lake," said Rochelle Nason, executive director of the League to Save Lake Tahoe. "Specifically, we need to start examining boats as they enter the basin, before they make it to the shoreline. The day may come when Tahoe must be closed to traveling boats."