Tahoe Keys’ plan to control aquatic invasive plants combines the best available methods to gain control over the infestation and greatly reduce the spread of these invasive species.
Integrated Management Plan
Building on the Nonpoint Source Plan and other existing work, the Tahoe Keys Property Owners Association developed an Integrated Management Plan using rigorous scientific study and evaluation along with an inclusive collaborative process consulting numerous independent experts, consultants and agencies.
Designed to be adaptive and responsive to both results in the field and potential new control methods, the Integrated Management Plan brings a wide range of tools to bear on the aquatic plant infestation.
These methods have proven successful in other similar bodies of water around the country and in controlled laboratory reproductions of Tahoe Keys conditions.
The next step in evaluating these methods is a small-scale Integrated Control Methods Test in the Tahoe Keys.
The Association didn’t set out with any method – including herbicides – as a predetermined or desired outcome. Evaluation, the urgency to gain control over the plants quickly and input from experts lead to the conclusion that the proposed plan is the best and only option.
A limited (in size and duration) application of herbicides is a small but critical part of the plan to bring the plants under control to a level that other methods could keep them under control.
Control vs. Eradication
Total elimination of the invasive weeds is likely impossible, due to source banks (seeds and other materials buried in the sediment that could regrow) and ongoing re-introduction from other parts of Lake Tahoe.
But by reducing the weeds’ volume significantly, they become much easier to control, minimizing the impacts of control methods, and become much less likely to spread from the Tahoe Keys lagoons to the greater Lake Tahoe area.
Control also helps:
In addition to continuing to refine existing methods including harvesting, fragment collection and bottom barriers, a range of other methods are planned or under consideration.
Diver-Assisted Hand Pulling
Trained SCUBA divers can selectively target invasive plants, removing the majority of the plants from a treated area. Also most effective in smaller areas, diver-assisted removal may be useful in targeted locations. However, increased equipment support activities that interfere with navigation, diver safety, and turbidity can be negative aspects of these operations.
Laminar Flow Aeration
Air is bubbled up in a laminar flow from the bottom through the water column to bring proper oxygenation to the water closer to the bottom of the lagoons, which has been reduced by aquatic invasive plants. Trail aeration will evaluate benefits to the ecosystem and sediment.
UV light is a newly identified, still experimental method that may be found to help kill aquatic invasive weeds in the Tahoe Keys. There is a trial planned for Lakeside Marina, and the Association has pledged support for a small-scale test in the Tahoe Keys lagoons.
The association is evaluating the selective use of herbicides in the most impacted areas within the lagoons. When used properly by licensed applicators, herbicides are non-toxic to fish, wildlife and humans, only targeting the specific invasive plants. Although currently approved for use by the Environmental Protection Agency, the association would need permission from regional agencies (e.g., Lahontan Regional Water Quality Control Board) before implementing this control measure.
Herbicides being evaluated, along with proposed application concentrations:
Triclopyr: 1 part per million
Endothall: 2 parts per million
Penoxsulan: 5 parts per billion
The use of herbicides as part of an integrated plan has been endorsed by an array of independent national and regional experts, including Dr. Pat Akers with the California Department of Food and Agriculture, Dr. Joe DiTomaso of UC Davis, Dr. Kurt Getsinger with the U.S. Army Corps of Engineers, Dr. Sudeep Chandra with University of Nevada, Reno and Joel Trumbo with the California Department of Fish and Wildlife.
Other lakes and bodies of water have successfully used these herbicides to control aquatic invasive plants without harming native species or posing public health risks to drinking water supplies, including Discovery Bay south of the California Delta, Big Bear Lake in Southern California, Clear Lake in Northern California, Loomis Lake in Washington, and numerous areas within the Sacramento-San Joaquin Delta.
Comprehensive dye studies conducted in 2011 and again in 2016 were used to assess how herbicides would move in the lagoons during the trial period. The studies revealed that water movement within the lagoons is very limited, especially in the back lagoons where several of the proposed demonstration sites are located.
All of the herbicides break down by light, microbial action and other processes, typically degrading to non-detectable levels within a few days to two weeks.