Image: Scientists with Asian clams
Randy Pench  /  The Sacramento Bee via AP
UC Davis research scientists Brant Allen, left, and Marion Wittmann with a handful of Asian clams removed from the bottom of Lake Tahoe.
updated 7/10/2010 8:10:19 PM ET 2010-07-11T00:10:19

Scuba-diving scientists are unrolling long rubber mats across the bottom of Lake Tahoe coves in an attempt to quell a clam invasion that could cloud the world-reknown cobalt waters.

The half-acre mats are designed to smother dime-sized nonnative Asian clams that can reach populations of 5,000 per square yard.

Geoffrey Schladow, director of the Tahoe Environmental Research Center run by the University of California, Davis, said the clams promote so much algae growth that they can turn some coves from blue to green.

"They suck in the water and they filter out the algae. Their excretions are highly concentrated packages of nutrients," he said.

The scientists carpeted one south shore bay with the rubber mats on Friday. They plan to cover another half-acre soon.

The bottom coverings will remain in place all summer, then will be removed to see if the clams return.

The rubber mat experiment will consume nearly half the $1.4 million budgeted for clam-eradication efforts at the lake. The U.S. Fish and Wildlife Service and the Tahoe Regional Planning Agency are seeking another $4 million to continue the battle.

Image: Mat lowered into water
Randy Pench  /  The Sacramento Bee via AP
Workers lower one of eight rubber rolls into 15-feet of water at Marla Bay near Zephyr Cove, Nev., on Friday.

The clams were first found in 2002 in the Sierra Nevada lake that straddles the California-Nevada border, after they were likely inadvertently brought in by boaters. Scientists fear the clams could change the lake's chemistry, opening the door to other invasive species.

Officials are also trying to eliminate infestations of two nonnative plants, the Eurasian Water Milfoil and Curly Leaf Pondweed. They set up four roadside inspection stations two years ago and ordered inspections of all boats entering the water in an attempt to keep out other foreign species, particularly quagga mussels and New Zealand mud snails.

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