Workshop on proposed solutions to stop spread of invasive plants in Lake Tahoe

SOUTH LAKE TAHOE, Calif. - The Tahoe Keys Property Owners Association (TKPOA) and its partners are seeking public input on potential solutions to the spread of aquatic weeds that currently threaten all of Lake Tahoe. They are holding a meeting on Friday, October 29 from 3:00 p.m. - 6:00 p.m. at the Tahoe Keys Pavilion, 300-498 Ala Wai Blvd, South Lake Tahoe.

A proposed permit for an aquatic weeds control methods test (National Pollutant Discharge Elimination System or NPDES) prescribing various treatment options is currently under consideration before the Lahontan Water Board.

The Control Methods Test application proposes the stand-alone and combined use of various approaches including targeted herbicides and UV-C light to reduce and control the abundant growth of invasive and nuisance aquatic weeds.

“The CMT will help determine the most effective, integrated management methods that will greatly reduce the impacts and threats of invasive aquatic plants on Lake Tahoe as well as improve management in the Tahoe Keys lagoons,” said Dr. Lars Anderson, an aquatic ecology/invasive species specialist and an affiliate of the University of California, Davis Weed Science Group. “The herbicides in the CMT are specifically chosen to control the target aquatic weeds while minimizing impacts to desirable native plants that are currently being suppressed by the invasive weeds. This approach has been used successfully in lakes throughout the U.S. that have the same species of invasive and nuisance plants.”

The UV-C light is a new technology shown to have some success in small test areas of Lake Tahoe but has not been tested on a large-scale area with water quality conditions like the Tahoe Keys lagoons.

Anderson is a retired aquatic plant biologist who ran the USDA lab at UC Davis. He is now helping the Tahoe Keys. He started working and surveying the area in 1995 and recognized the problem right away. He said the plants would spread if there was no effective management.

Exactly how the invasive plants made their way into the lake is unknown, but it can be assumed they made their way from the Sacramento Delta on boats. This could have happened as long ago as the 1940s and 50s before people were aware of them.

"People don't notice until they are a problem as they grow out of sight," said Anderson.

He has been trying to give solutions since 1995. Anderson said the collaboration now between the League to Save Lake Tahoe, the TKPOA and Tahoe Regional Planning Agency will hopefully get a solution for removing the weeds. He said he is encouraged as there is now more realization of the problem.

"You can't do the same thing as always been doing and expect a new result," said Anderson.

What that solution will be isn't exactly known yet, that there is no 'silver bullet,' but Anderson said it will be a combination of methods.

"The Keys is unique to other areas," added Anderson

These invasive plants are difficult to control with no natural enemies. They can fragment and spread seeds which makes digging them out not a valid solution.

The curly-leaf pondweed is one of the newer invasive plants in Tahoe and has expanded quickly like the Eurasian Milfoil. It gets a head start on spreading as it forms a turion (shoot), sprouts, and waits for spring light so it's ready to go.

A third plant that is a problem is actually native to Lake Tahoe, the hornwort. It grows all over the world and likes warmer water that doesn't move. It has no roots so gets its nutrients from sediment along the water. It can grow down to 20-30 feet but is more common in the first 8-12 feet below the surface. As the water recedes, they grow faster as there is more light.

The control methods will use UV light alone in some spots, herbicides alone in other areas, with a third test using a combination of the two. UV takes a while to move around docks and is more efficient further out from shore and docks, which herbicide works better closer to shore, Anderson said.

Another method, laminator flow aeration, creates oxygenation at bottom of the lake which reduces the level of nutrients for algae, but it hasn't been tested on other species.

The League to Save Lake Tahoe strongly supports the proposed Control Methods Test because science clearly shows that aquatic weeds pose a dire threat, the status quo will not solve the problem, and the fate of Lake Tahoe is at stake.

"To Keep Tahoe Blue, we must move forward with this comprehensive and careful test of any and all methods that could be part of the long-term solution," said Darcie Goodman Collins, Ph.D., chief executive officer of the League to Save Lake Tahoe / Keep Tahoe Blue. "This fact is beyond debate: if we do nothing, or fail to act quickly, the worst fate for Lake Tahoe is unavoidable."

There are 170 acres of channels in the Tahoe Keys. The plan under review is to use the herbicide on less than 17 acres, and the other two methods on the rest.

The use of herbicide has been very successful in the U.S. before Anderson said. TKPOA couldn't get the approval of it before as the Lahontan Water Board prohibited the introduction of chemicals into the lake. The Environmental Protection Agency and State Water Board have changed their stance and a look at new things to remove the invasive weeks is allowed.

If approved, this is a three-year project with the first year taking a look at the effect of herbicides and the combinations, They then monitor the area for two years and look at the results. They will then propose to expand the processes and try to figure out the most efficient and best at keeping things under control. They will evaluate how fast the herbicides break down/

"Lots of precautions will be taken," said Anderson.

The Oct. 29 workshop will provide background on the project – its history, goals, challenges, potential solutions, and timeline while soliciting input from the community. The open house format will include various stations where attendees can review information, ask questions, and provide input throughout the morning. Representatives of various agencies, as well as some leading scientific experts involved in the project, will provide information and be available to address questions and take comments. More information will be available on https://tahoekeysweeds.org/.

Aquatic weeds have spread to many areas around Lake Tahoe creating an urgency and necessity for lake-wide collaboration to control them, with the greatest concentration being found in the Tahoe Keys. The Tahoe Keys Property Owners Association submitted the Aquatic Weed Control Methods Test application, which required an Environmental Impact Report (EIR) per the California Environmental Quality Act (CEQA) by Lahontan Regional Water Quality Control Board (Lahontan Water Board), and an Environmental Impact Statement (EIS) per the Tahoe Basin Compact by the Tahoe Regional Planning Agency (TRPA). Both the EIR and EIS are available at (www.waterboards.ca.gov/lahontan/water_issues/programs/tahoe_keys_weed_control).

Since the 1980s, TKPOA has invested millions of dollars to combat AIS and worked with prominent regulatory bodies and the League to Save Lake Tahoe on numerous concepts including weed harvesting, fragment collection, bottom barriers, bubble curtains, and supported research on other new methods. The agencies have mobilized their staffs in support and matched the TKPOA investment. This joint effort now enters a critical period. The public comment period on the draft permit, which began Sept. 15 and ends Nov. 1, 2021, will be considered by the Tahoe Regional Planning Agency Board (TRPA) and the Lahontan Regional Water Quality Control Board (LRWQCB) in January. If approved, testing would start in the spring of 2022, depending on water levels and other natural factors.

The invasive plant spread throughout the lake is compromising water quality, degrading recreational uses, as well as threatening the future ecosystem of Lake Tahoe, which is one of only a few federally designated Outstanding National Resource Water bodies in the U.S.

The effects of climate change on the ecosystem are adding to the urgency. In just five decades, Tahoe’s average water temperature has increased 1.4 degrees Fahrenheit. Dr. Anderson explained that the combination of milder winters, early spring warming, and now drought conditions have together exacerbated the invasive nuisance aquatic weed and algae (cyanobacteria) conditions.

The Lahontan Regional Water Quality Control Board is accepting written public comments on the Control Methods Test permit until 5 p.m. Nov. 1, 2021. Comment letters may be submitted electronically, via emails, with the subject "Tahoe Keys Weeds Control Test" to the following e-mail address: lahontan@waterboard.ca.gov or submitted in hard copy to: 2501 Lake Tahoe Boulevard, South Lake Tahoe, CA 96150, to the attention of Russell Norman.