Herbicides considered to control invasive aquatic plants in Tahoe Keys

Desperate to control aquatic invasive species in a busy Lake Tahoe waterway, two regulators are considering allowing the use of aquatic herbicides in the Tahoe Basin, a treatment method that was heretofore banned.

The Tahoe Regional Planning Agency Board of Directors and the Lahontan Region Water Quality Control Board will decide in January whether herbicides should be used on 17 acres in the Tahoe Keys to control the rapid spread of invasive underwater plants. Invasive aquatic plants have the potential to devastate Tahoe by affecting lake clarity, preventing boating, negatively affecting aquatic life, and contributing to algal blooms.

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Advocates argue that Tahoe’s aquatic invasive species problem is reaching critical proportions and that federally approved herbicides could help. Opponents argue that they are not working and that areas infested with invasive species such as the Tahoe Keys should be isolated from the rest of the lake.

Both parties agree that something must be done.

“This fact is indisputable: if we do nothing, or if we do not act quickly, the worst fate for Lake Tahoe is inevitable,” said Darcie Goodman Collins, executive director of the League to Save Lake Tahoe.

A threat to the clarity and health of Lake Tahoe

Located in South Lake Tahoe, the Tahoe Keys Lagoons were built in the 1960s on the Upper River Marsh. The swamp was excavated and the ground was covered with sand to form stable construction sites. Les Clés now includes more than 1,500 housing units; 900 docks; and several businesses surrounded by 172 acres of waterways.

Invasive aquatic weeds thrive in lagoons due to the relative warmth of the water and its stagnant, shallow water that lets in light for weed growth. The Lahontan Regional Water Quality Control Council estimates that around 90% of the lagoons are infested with aquatic weeds. Weeds are also easily spread by boat propellers which fragment the plants and scatter in pieces around the lake.

The Keys is a boating community with a large number of vacation rentals and more boat trips in and out of the waterways than many other areas around the lake – about 25% of the lake’s commercial, government and private boats use the waterways. Keys. Boats leaving the Keys are the main source of new infestations in other parts of the lake.

Aquatic invasive species have been rampant in the Keys since the 1970s. Since the mid-1980s, seasonal mowing has been the primary weed control practice to keep waterways clear for boats, but mowing has been a temporary solution. – it does not actually reduce the amount of aquatic weeds growing in the Keys.

More than 10,000 cubic meters of plant material – over 900 dump trucks – are removed each year, costing the Tahoe Keys Property Owners Association up to $ 400,000 per year.

The association tried to cover parts of the Keys with lower barriers – rugs that keep sunlight from reaching weeds – but the association is only allowed to use five acres of lower barriers at a time per the Lahontan Regional Water Quality Board, a challenge when managing 172 acres of waterways. The association has spent approximately $ 5.7 million on weed control over the years.

Now, the association is asking for a waiver of a previous herbicide ban in the region that would allow a three-year trial period in the Tahoe Keys.

Lake Tahoe and the adjacent Tahoe Keys are recognized as federally protected from herbicide use because of their exceptional quality and recreational importance. Aquatic herbicides have never been used in Lake Tahoe or the Keys.

The trial project would combine herbicides, UV light exposure, manual extraction and other methods with the ultimate goal of eliminating 75% of the invasive plants on the 17 acres over a three-year period, according to Lars Anderson, a retiree from the US Department of Aquatic Plant and Agricultural Invasive Species Biologist.

Supporters of the project, including scientists from the Tahoe Environmental Research Center; University of California, Davis; University of Nevada, Reno; the League to Save Lake Tahoe; and the Tahoe Resource Conservation District.

They claim that the herbicides approved by the Environmental Protection Agency have been used for decades in the United States and that they only impact target invasive plants. Herbicides proposed for the Tahoe Keys area target three weed species common in the Keys: curly-leaved pondweed, Eurasian watermilfoil and coontail.

In small trials, selective herbicides have been shown to kill invasive plants without harming native plants, Anderson said. In addition, underwater curtains will be installed to prevent water from treated areas from spilling into other parts of the Keys and the lake.

“I don’t think the test poses any risk to Tahoe, even if it involves herbicides,” said Jesse Patterson, a former marine biologist who now works as a strategy officer for the League to Save Lake Tahoe. The League has previously opposed the use of herbicides on the lake, but Patterson said the limited and controlled nature of the trial had allayed many of the League’s concerns. “I know herbicides are one of them and getting the most attention, but it’s a larger suite of tools. “

Bottom barrier installation is underway in Taylor and Tallac Marshes as part of the largest invasive aquatic plant removal project in Lake Tahoe.

Another solution proposed by opponents of the herbicide

Opponents such as the Tahoe Area Sierra Club, the Friends of the West Shore and the California Sportfishing Protection Alliance argue that herbicides are not a viable long-term solution and will clog the lake and drinking water.

Instead, the Sierra Club’s Tahoe Area Group is pushing for an alternative solution: isolate the Tahoe Keys from the main lake. The houses could remain, but the lagoon’s return to native swamps would filter out pollutants, the group said.

“Herbicides do nothing to address the problem: nutrients and sediment in the water,” said Tobi Tyler, vice president of the Tahoe Area Group at the Sierra Club and former water resources engineer at Lahontan Regional Water Quality Control. Board. “Making sure Keys owners can get their boats out of their backyard is more important than saving the lake?” “

“Do people want this? No. They basically understand that this is a natural treasure and a world famous lake. They understand that this is a special lake and you don’t just pour herbicides in here… It’s not about treating this lake in a way that it should be.

The Tahoe Keys debate takes place as other agencies team up to complete the largest invasive plant removal project to date in the lake itself.

The US Lake Tahoe Basin Management Unit and the Tahoe Regional Planning Agency are removing 17 acres of invasive plants in Taylor and Tallac creeks and marshes by staking bottom barriers (large tarps) on the marsh floor from Tallac.

Lahontan’s regional water quality control council is expected to vote on the issue on January 12. The board of the Tahoe Regional Planning Agency is expected to vote on the issue on Jan.26.

Amy Alonzo covers the Outdoors, Recreation, and Environment for Nevada and Lake Tahoe. Contact her at [email protected] Here’s how you can support continuous coverage and local journalism.

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