Control Methods Test

Overall, the CMT Year 1 was successfully implemented as planned. Preliminary data show the herbicides have responded as expected. All the details for Year 1 can be found in the implementation report published September 30, 2022.

Year 2 design will be assessing which treatment sites from Year 1 have shown success and what non-herbicide methods can be used to maintain a 75% reduction in biovolume of the weeds. Using the three Group B methods – bottom barriers, diver hand pulling, and UV-C – we will spot treat sites that show regrowth to stifle the returning weeds. There will be water quality monitoring and sampling around the lagoons to look at long-term effects of herbicide use and other treatment methods. There will not be any additional herbicide application or boating restrictions!

Group B methods are non-herbicide treatment techniques used for the goal of maintaining a 75% reduction in biovolume of the weeds after herbicide treatment. The three methods being tested are: bottom barriers, diver assisted hand pulling, and UV-C.

There will be no herbicide application and therefore no restrictions in Years 2 and 3.

The budget for Year 2 of the CMT is $1.1 Million. The $1.1M cost will be funded by a projected $350,000 surplus from the Year 1 assessment, $100K from the Mitigation Fund managed by Tahoe Regional Planning Agency (TRPA) and Lahontan Regional Water Quality Board (LRWQB), and a $650,000 assessment subject to member approval. The $650,000 net funding translates into a $442 assessment for waterfront owners and $221 for landlocked properties. This will fund Group B methods, project management, reporting, monitoring, supplies, and staffing.

Funding for Year 2 is broken up into four main categories:

1) Consulting services for Project Management plus compliance, reporting, and a modest investment in the long-term solution.

2) Two of the three Group B methods: bottom barriers and diver hand pulling.

3) Field supplies for monitoring and treatment.

4) An allocation to WQ payroll for TKPOA’s AIS technicians.

The UV-C treatments will be funded by TRPA.

The Mitigation Fund is an account that our homeowners financed in the 1990’s. It is managed by both the Tahoe Regional Planning Agency (TRPA) and Lahontan Regional Water Quality Board (LRWQB). The fund is used for projects around Lake Tahoe for nutrient mitigation. The TKPOA will ask the regulatory agencies to release $100k to support our efforts to help improve water quality in the lagoons.

The Year 2 design is keeping budget at the forefront. We have an agreement with our partners that we will scale the treatments to be effective within the fixed budget. Using the implementation units as a form of measurement allows us to quantify each treatment method to plot the direction moving forward. With this methodology of approach, we expect that the money will be allocated efficiently and appropriately to ensure no cost overruns occur. A $200k contingency is built into the budget for unexpected expenses that have not been accounted for.

Currently data analysis is being done on the many thousands of samples and data points collected over the Year 1 season. Preliminary results show that the herbicides are working as expected in each treatment site. More conclusive data will be shared in the Winter report.

The herbicides used (Endothall and Triclopyr) target specific weed species. Endothall is effective against all three nuisance varieties – Eurasian Milfoil, Curly Leaf Pondweed, and Coontail – but does not harm native species such as Elodia. Triclopyr is specific to Eurasian Milfoil, therefore other aquatic weeds, nuisance and native, will continue to grow. Triclopyr is an important prospective tool as it likely has long-lasting impact against Milfoil, which is an invasive species along the shorelines of our lagoons. The goal is to contain the invasive weeds (and Coontail), while allowing desired natives to continue to grow. We want the ecosystem to return to a natural state, so thriving native plants is a sign of success.

The CMT was designed (and permitted) to be a 3-year test. In effect, we are comparing the results of a single application of herbicide followed by two years of spot treatments against the results of three years of UV-C treatment and three years of Laminar Flow Aeration. If we stop now, there will be no comparison and no recommended control strategy. Preliminary Year 1 results are promising, but it is necessary to collect data from Years 2 and 3 to be able to reach a consensus direction for a long-term control of invasive weeds.

Year 3 is expected to look similar to Year 2. We project another $1.1 million will be needed in 2024 to complete the final phase of the CMT. Implementation will focus on follow-up treatment in sites that have shown the most success in the first two years, as well as continuation of Laminar Flow Aeration and UV-C treatment. This current referendum does not include any funding for Year 3. Year 3 funding will come from either a one-time adjustment to standard quarterly assessments or another special assessment voted on by the membership. Again, there will not be any additional herbicide application or boating restrictions in Year 3!

The WQ Team believes that the long-term solution for controlling invasive weeds and improving water quality in the lagoons will include the circulation system in conjunction with the control methods that are determined by the CMT. Currently the circulation system is non-functioning and likely requires significant repairs and possible upgrades. The CMT budget for Year 2 includes a modest effort to evaluate the circulation system.

No, only to assess what it will take to make the system operational. There is still research needed to determine the potential for the success of improving water quality by making such an investment. The research will include a financial assessment of various options. TKPOA members would be voting on any proposal that requires significant investment of TKPOA funds.

The TRPA and League to Save Lake Tahoe are committed partners with the TKPOA, working to find a permittable solution for the invasive weeds and improved water quality in our lagoons. The TRPA has invested approximately $8 million in the CMT, and will continue to support the effort going forward. They have fully funded the UV-C treatment project, most of the monitoring activities, virtually all of the laboratory analysis, and the critical environmental impact analysis. In 2018, the League gave a $100k grant to the TKPOA, and has proposed another $100k for 2022-25. These funds have helped support the Laminar Flow Aeration (LFA) project and fragment control methods which includes the Double Bubble Curtains in the East and West channels. Beyond the financial stake, The League’s support as the leading, local private environmental group has been instrumental in gaining support from stakeholders around the lake. These fundamental partnerships are essential to the future of the Keys’ lagoons.

• In the spring when snow melt causes the lake to rise, water typically flows into the Keys through the West and East channels as there are no streams flowing into the lagoons.  Alternatively, when the lake level starts to drop, water might be observed flowing from the Keys into Lake Tahoe, usually after June.

• This is a test of methods, notably herbicide, UV-C light, and laminar flow aeration (LFA).  The number and size of test sites reflect what the scientists who designed the test determined was necessary to achieve scientifically significant results.

• The test was designed by a team of scientists looking for test areas that are representative of the aquatic plants and other conditions throughout the lagoons
• Consideration was given to area, weed volume, aquatic plant species mix, water depth, distance from the lake, surrounding terrain (e.g., docks and rocks), and other variables.

• Please see link to the TKPOA Water Quality Department website for more information on the herbicides that will be used:  https://www.keysweedsmanagement.org/cmt-project
• The aquatic herbicides being used are Federal and CA EPA approved, and are used in drinking water reservoirs, recreation lakes, and environmentally sensitive water bodies.  Application of the herbicides will be done by trained technicians under strict BMP’s.  The proposed herbicides are not a threat to humans, pets, fish, or wildlife, even inside the treatment test areas.
• The selected herbicides are selective, and only target invasive species.
• The restriction on water activities is driven in part by the fact that there are 25 different test sites, and we must avoid any cross-contamination between the individual sites in order to obtain scientifically valid results.
• Also, the permit requires hydrologic conditions (net inflow from lake to lagoons) and in-water barriers (double turbidity curtains) that essentially reduce to zero the chance of detectable levels of aquatic herbicide or their degradants reaching the lake.

• Combined, the area of the West Lagoon (private residences) and the East Lagoon (which includes the Tahoe Keys Marina) is approximately 170 acres.  The herbicides will be tested in 17 acres, or about 10% of the Keys.  Overall, there are 42 acres of test sites, including 5.5 acres of “control”.   More details can be found in table 2 on page 26 of the Aquatic Pesticide Application Plan (APAP) at https://www.keysweedsmanagement.org/cmt-project

• The TKPOA Water Quality department has a tab on its website dedicated to the CMT.  It can be found at:  https://www.keysweedsmanagement.org/cmt-project
• The Tahoe Regional Planning Agency has also created a website with extensive information on the history of the invasive weeds in Lake Tahoe, the collaborative effort to combat aquatic invasive species, the environmental analyses, and more.  It can be found at: https://tahoekeysweeds.org/

• The TKPOA and the agencies working with us on the CMT assume that the results of the test will instruct us on how to use these tools (aquatic herbicide, UV-C light treatment, and laminar flow aeration) on a large scale in the near future.

• As/if/when there is a large-scale application of herbicide, we would anticipate that the timing, logistics, and restrictions would be similar to those we face this spring.
• The results of the CMT will define what the next steps are in terms of treatment.  It is expected that there would be another environmental impact analysis (EIR/EIS) and another round of permit applications for a specific treatment plan.

• The test will inform on the effectiveness of the various control methods, individually and in combination. The results will shape the TKPOA’s next steps for future treatment. 
• It is not expected that herbicides or any of the treatment methods alone will solve the weeds problem and address deteriorating water quality in the Keys.  The ultimate solution will likely use some or all of the tools tested in the CMT, but as part of “system” that includes circulation and filtration of water within the lagoons.
• Harvesting has been effective in keeping the navigation lanes open and removing large quantities of biomass each year, but harvesting is not a good long-term solution.  Fragments are a problem, and “mowing” the invasive weeds appears to stimulate seasonal growth.  The TKPOA has been and will continue to look for alternatives to harvesting.
• While the CMT is a 3-year test, the TKPOA is hopeful that we can begin working toward a long-term comprehensive water quality program in 2023 in parallel.

• SEA and UNR prepared draft reports on UV-C treatments in 2021.  They have not yet been published.
• Due to logistical challenges with the treatment boats and the fires last summer, the testing results were limited.

• UV-C treatment does not require closing the waterways.  It is the herbicide application that is driving the need for turbidity curtains, extensive monitoring of water quality, and the closure.  In year 1 of the test, there are UV-C sites within the “test areas." In years 2 and 3 of the CMT, there will be no herbicide treatment, hence no closures.

• The herbicides are being applied at about half of the maximum Federal and CA EPA approved application rates. Higher concentrations won’t be needed because contact time of the herbicide with the plants will be sufficient in the still lagoon waters.
• In the UV-C/herbicide “combo” sites, herbicides will be used along the shoreline and UV-C treatment in the navigation lanes.  This results in an herbicide application rate that is a very small fraction of the maximum rate.