Invasive plants are invading Tahoe. A debate rages over using herbicides to battle them

Article from Reno Gazette Journel.

https://www.rgj.com/story/news/2021/12/22/herbicides-considered-battle-aquatic-invasive-plants-tahoe-keys/8977684002/

Amy Alonzo
Published 11:52 am Dec. 22, 2021. Updaed 11:39 am PT Dec. 23, 2021

Desperate to control aquatic invasive species in a heavily traveled Lake Tahoe waterway, two regulatory agencies are considering allowing the use of aquatic herbicides in the Tahoe Basin, a treatment method that up until now has been prohibited.

The Tahoe Regional Planning Agency Governing Board and the Lahontan Regional Water Quality Control Board will decide in January if herbicides should be used on 17 acres in the Tahoe Keys to control rapidly spreading underwater invasive plants. Aquatic invasive plants have the potential to devastate Tahoe by impacting lake clarity, impeding boating, negatively affecting aquatic life and contributing to algae blooms.

Advocates argue Tahoe’s invasive aquatic species problem is reaching crisis proportions and that federally approved herbicides could help. Opponents argue they don’t work and that invasive species-plagued areas such as the Tahoe Keys should be walled off from the rest of the lake.

Both sides agree something must be done.

“This fact is beyond debate: If we do nothing, or fail to act quickly, the worst fate for Lake Tahoe is unavoidable,” said Darcie Goodman Collins, chief executive officer of the League to Save Lake Tahoe.

A threat to Lake Tahoe’s clarity and health

Located in South Lake Tahoe, the Tahoe Keys Lagoons were built in the 1960’s on the Upper River Marsh. The marsh was excavated, and the soil was capped with sand to form stable building sites. The Keys now include more than 1,500 housing units; 900 docks; and several businesses surrounded by 172 acres of waterways.

Invasive aquatic weeds thrive in the Lagoons because of the water’s relative warmth and its stagnant, shallow water that allows light in for weed growth. It is estimated by the Lahontan Regional Water Quality Control Board that about 90% of the lagoons are infested with aquatic weeds. The weeds also spread easily by boat propellers that fragment the plants, spreading pieces around the lake.

The Keys is a boating community with more boat trips in and out of the waterways than many other areas around the lake — an estimated 25% of the lake’s commercial, government and private boats use the Keys.

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

More than 10,000 cubic yards of plant matter — more than 900 dump trucks — are removed annually, costing the Tahoe Keys Property Owners Association up to $400,000 per year.
The Tahoe Keys, a development of 1,500 homes along manmade canals on the south shore of Lake Tahoe.

The association has tried lining portions of the Keys with bottom barriers — mats that prevent sunlight from reaching the weeds — but the association is only permitted to use five acres of bottom barriers at a time by the Lahontan Regional Water Quality Board, a challenge when managing 172 acres of waterways. The association has spent roughly $5.7 million on weed control over the years.

Now, the association is asking for an exemption to a previous ban on herbicides in the area that would allow a three-year trial period in the Tahoe Keys.

Lake Tahoe, and the adjoining Tahoe Keys, is recognized as federally protected from the use of herbicides because of its exceptional quality and recreational significance. 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 an end goal of removing 75% of the invasive plants on the 17 acres over the three-year period, according to Lars Anderson, a retired United States Department of Agriculture aquatic plant and invasive species biologist.

Supporters of the project including scientists at 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 argue that the Environmental Protection Agency-approved herbicides have been used for decades throughout the United States and that they only impact the targeted invasive plants. The herbicides proposed for the Tahoe Keys area target three species of weeds prevalent in the Keys: Curlyleaf pondweed, Eurasian watermilfoil and coontail.

In small trials, the selective herbicides have shown they kill the invasive plants without harming native plants, Anderson said. In addition, underwater curtains will be put in to keep water from treated areas from spreading into other parts of the Keys and the Lake.

“I don’t believe the test poses any risk to Tahoe, even though it involves herbicides,” said Jesse Patterson, a former marine biologist who now works as the chief strategy officer for the League to Save Lake Tahoe. The League has previously opposed herbicide use at the lake, but Patterson said the limited and controlled nature of the trial has assuaged many of the League’s concerns. “I know herbicides are part of it and are getting the most attention, but it’s a broader suite of tools.”

Another solution proposed by opponents to herbicide

Opponents such as the Tahoe Area Sierra Club, Friends of West Shore and the California Sportfishing Protection Alliance argue herbicides aren’t a viable long-term solution and will foul the lake and drinking water.

The Tahoe Area Group of the Sierra Club is instead pushing for an alternate solution: Walling off the Tahoe Keys from the main lake. The houses could remain but returning the lagoon to native marshland would filter out pollutants, according to the group.

“Herbicides do nothing about the problem: the nutrients and the sediment in the water,” said Tobi Tyler, Vice Chair of the Tahoe Area Group of the Sierra Club and a former water resource engineer with the Lahontan Regional Water Quality Control Board. “Making sure the Keys homeowners can take their boats out of their backyards is more important than saving the lake?”

“Do people want this? No. They understand fundamentally that this is a natural treasure and world-renowned lake. They get that this is a special lake and you don’t just pour herbicides in here … This is not treating this lake in a manner it should be treated.”

The Tahoe Keys debate takes place as other agencies are partnering to perform the largest invasive plant removal project to date in the Lake itself.

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