By Jeff Delong, Reno Gazette-Journal

A troublesome water weed that has spread through Lake Tahoe for decades is now established along the length of the Truckee River, posing possible problems of unknown scope and scale.

From the outlet of the Tahoe City Dam to where the river flows into Pyramid Lake 116 miles downstream in the desert, anywhere the river’s waters flow slowly enough Eurasian watermilfoil can be found, experts said.

“It goes all the way to the end of the river,” said John Mosely, environmental director of the Pyramid Lake Paiute Tribe. “In every irrigation diversion, in every backwater, we can find it.

“It’s a huge concern,” Mosely said.

An exotic and aggressive invader, Eurasian watermilfoil is trouble. The weed crowds out native plants and takes away oxygen needed by fish. It can ruin boating and clog irrigation ditches, water intakes and pipes.

No one knows for sure when it first showed up in Lake Tahoe.

A good guess is that watermilfoil appeared in South Lake Tahoe’s Tahoe Keys Marina – a place now thoroughly infested – sometime in the mid- to-late-1980s, said Lars Anderson, a scientist with the U.S. Department of Agriculture who has tracked the weed’s spread since 1994.

Spread by boats or as weed fragments carried by currents took root on the lake bottom, Eurasian watermilfoil can now be found in most of Tahoe’s marinas and some other near-shore areas.

Established near the Tahoe City Dam, the weed may have escaped into an overflowing Truckee River during the flood of January 1997.

It was found growing in a quiet part of the river near Verdi a few years later and is now firmly established in the lower river near Pyramid Lake.

The weed has not yet posed any serious problems for the Truckee Meadows Water Authority, which draws the bulk of its drinking water supplies from the river.

The utility’s hydroelectric plants are located in parts of the river that flow too fast for the weed to grow.

Recent multimillion-dollar upgrades to the Highland Canal, which serves the area’s primary drinking water treatment plant, substantially increased water velocity and diminished any threat, said Bill Hauck, water supply coordinator for the authority.A troublesome water weed that has spread through Lake Tahoe for decades is now established along the length of the Truckee River, posing possible problems of unknown scope and scale.

From the outlet of the Tahoe City Dam to where the river flows into Pyramid Lake 116 miles downstream in the desert, anywhere the river’s waters flow slowly enough Eurasian watermilfoil can be found, experts said.

“It goes all the way to the end of the river,” said John Mosely, environmental director of the Pyramid Lake Paiute Tribe. “In every irrigation diversion, in every backwater, we can find it.

“It’s a huge concern,” Mosely said.

An exotic and aggressive invader, Eurasian watermilfoil is trouble. The weed crowds out native plants and takes away oxygen needed by fish. It can ruin boating and clog irrigation ditches, water intakes and pipes.

No one knows for sure when it first showed up in Lake Tahoe.

A good guess is that watermilfoil appeared in South Lake Tahoe’s Tahoe Keys Marina – a place now thoroughly infested – sometime in the mid- to-late-1980s, said Lars Anderson, a scientist with the U.S. Department of Agriculture who has tracked the weed’s spread since 1994.

Spread by boats or as weed fragments carried by currents took root on the lake bottom, Eurasian watermilfoil can now be found in most of Tahoe’s marinas and some other near-shore areas.

Established near the Tahoe City Dam, the weed may have escaped into an overflowing Truckee River during the flood of January 1997.

It was found growing in a quiet part of the river near Verdi a few years later and is now firmly established in the lower river near Pyramid Lake.

The weed has not yet posed any serious problems for the Truckee Meadows Water Authority, which draws the bulk of its drinking water supplies from the river.

The utility’s hydroelectric plants are located in parts of the river that flow too fast for the weed to grow.

Recent multimillion-dollar upgrades to the Highland Canal, which serves the area’s primary drinking water treatment plant, substantially increased water velocity and diminished any threat, said Bill Hauck, water supply coordinator for the authority.