TRPA approves innovative invasive weeds test | SierraSun.com
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TRPA approves innovative invasive weeds test

The Tahoe Regional Planning Agency Governing Board yesterday unanimously approved a project to test innovative methods to address the largest infestation of invasive weeds in the Lake Tahoe Basin.

An infestation of aquatic invasive weeds in the Tahoe Keys lagoons in South Lake Tahoe is accelerating and poses a serious threat to Lake Tahoe if not controlled, according to Tahoe Regional Planning Agency. The Tahoe Keys Property Owners Association proposed the test project in targeted areas of the 170 acres of waterways. The area is approximately seven times greater than all other Lake Tahoe marinas combined.

The unanimous board vote clears the path for a combination of weed treatments including ultraviolet light, a one-time application of EPA-certified aquatic herbicides, and a process to aerate the lagoon bottom with small bubbles to reduce plant growth. The association worked with scientists, community members, environmental agencies, and non-profit organizations in a multi-year collaborative process that was thorough, scientifically rigorous, and inclusive, the agency said.



“If left unchecked, aquatic invasive weeds in any part of Lake Tahoe threaten our entire ecosystem,” Tahoe Regional Planning Agency Executive Director Joanne S. Marchetta said. “With climate change increasing water temperatures, we have an urgent need to deploy science-based solutions to combat these emergent threats.”

Aquatic weeds cover more than 90% of the Tahoe Keys lagoons and provide sources of continuing infestations around the lake including popular recreation areas like Emerald Bay. Treating the Tahoe Keys lagoons is the number one priority for the multi-agency Lake Tahoe Aquatic Invasive Species Coordinating Committee.



Following decades of failed attempts to control the weeds with conventional methods, in 2017 the Tahoe Keys Property Owners Association applied to water quality agencies for a permit to explore what tools might “knock back” the infestation to a controllable level so it can be maintained by non-herbicidal methods. The environmental analysis determined that Lake Tahoe is not at risk from this test of mixed methods.

“The Tahoe Keys Property Owners Association has been actively managing this weed infestation for over 40 years and has invested millions while the infestation has only gotten worse,” association president David Peterson said. “One method alone is not going to work. For the sake of the entire Lake Tahoe ecosystem, we need to test all tools to address the scale of the invasive species problems in the Tahoe Keys.”

UC Davis professor emeritus Dr. Charles Goldman was among the scientists to speak in support of the project yesterday. “Aquatic herbicides have come a long way and this is the appropriate measure at this time,” he said. Goldman famously sounded the alarm of Lake Tahoe’s declining clarity in the 1960s and his work prompted the states to create the bi-state Tahoe Regional Planning Agency to stop harmful development practices.

“Collaboration over the course of many years brought us to this important vote,” Marchetta said. “It’s yet another example that if we trust each other and rely on science, we can collectively make the best decisions to protect Lake Tahoe for future generations.”

Earlier this month, California’s Lahontan Regional Water Quality Control Board voted unanimously to certify the environmental analysis and issue a special permit for the project. Following the approval, testing and monitoring could begin in cordoned areas of the Tahoe Keys lagoons this spring. Learn more about the project at http://www.tahoekeysweeds.org.

Source: Tahoe Regional Planning Agency

A linear bubble curtain helps stop fragments of aquatic invasive weeds from leaving the lagoons. Smaller bubble patterns are from laminar flow aerators, which raise oxygen concentrations in the water column to increase the rate of decay and reduce the layer of organic material on the lake bed the plants use for nutrients.
Photo courtesy Sierra Overhead Analytics
The multiple methods control test could begin in Spring, 2022 with methods being tested in different areas for monitoring. Aquatic herbicides will be applied only once in areas closed off with double “turbidity” curtains.
Photo courtesy Tahoe Keys Property Owners Association

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