• The Challenge

    Aquatic invasive plants have taken root in shallow waters around Lake Tahoe, threatening the lake’s prized clarity, water quality, ecology, recreation and economy.

  • Why this is important

    Aquatic Invasive Plants are a Widespread Problem

    Around the Country

    USGS Map of Aquatic Invasive Plants, 2018

    Aquatic invasive plants are a challenge for numerous bodies of water around the country, costing billions of dollars each year, according the the US Fish and Wildlife Service. Click here to see how other areas around the west are handling the challenge.

    Around Lake Tahoe

    Bureau of Land Management Map of Aquatic Invasive Plants, 2017

     

    Aquatic invasive plants affect all marinas and numerous shallow, warm areas around Lake Tahoe and continue to spread, constituting the most immediate threat to Lake Tahoe, according to the University of Nevada, Reno's 2015 Implementation Plan for the Control of Aquatic Invasive Species within Lake Tahoe. Curlyleaf pondweed, able to grow in deeper, colder waters, has begun to spread more rapidly than Eurasian watermilfoil.

    In the Tahoe Keys

    Tahoe Keys Curlyleaf pondweed distribution map, 2016

     

    More than 95 percent of the Tahoe Keys' 172-acre lagoons are infested with aquatic invasive plants. Tahoe Keys Property Owners Association has both aggressively managed these plants with available methods and proactively sought long-term solutions to bring the infestation under control once and for all.

  • Why This is Important

    Harvesting is the primary control method available to the Tahoe Keys today. In 1984, roughly 100 cubic yards were removed from the lagoons and nearly 10,000 cubic yards were removed in 2017. In spite of these efforts, which cost $400,000 a year, Tahoe Keys Property Owners Association is clearly losing ground with these approved tools. Find out more about current efforts.

     

    At the same time, conditions in the lake are becoming more and more hospitable for these plants, with the UC Davis Tahoe Environmental Research Center 2017 State of the Lake Report showing the water warming 10x faster than normal.

     

    The continued spread of these aquatic invasive plants could rapidly transform from a nuisance to a very real threat to the environment, water quality, recreation and the economy of Lake Tahoe. These plants can harbor other non-native species and create ideal habitat for mosquitoes.

    History of Efforts

    We have been working to control the plants in the lagoons by looking for long-term, integrative solutions for decades, working with a broad-range of scientific experts, associations and agencies to vet an exhaustive list of potential plant control measures while examining and evaluating new techniques and technologies as they arise. .

     

    TKPOA is committed to solving the invasive plant problem and has so far spent $3,700,000 to manage the invasive plants and to develop improved methods. We're expected to spend another $2,500,000 by 2020. This funding comes from special assessments paid for by the property owners, along with grant funding and other private funding.

     

    The 1,500 Tahoe Keys property owners consistently support invasive plant management strategies in and out of the water including: Voting for a special assessment to continue funding the invasive plant management program.

    • Committing to Lake Friendly Landscaping and irrigation practices to protect water quality from nutrient runoff. 
    • Labeling all storm drains in Tahoe Keys to address and educate residents about nutrient runoff. 
    • The Water Quality Committee volunteers hundred of hours per year toward these efforts.

    TKPOA has collaborated with the Tahoe Regional Planning Agency, the Tahoe Resource Conservation District and US Forest Service since 2011. We have also worked with the League to Save Lake Tahoe to implement ways to prevent plant fragment spread.

    Integrative Methods

    Reducing the volume of weeds helps to ensure that other methods are more effective and fragments do not enter Lake Tahoe. TKPOA's best management practices that are used to reduce weeds include: ​

    • Harvesting and fragment collection: In 2017, TKPOA staff removed 9,996 cubic yards (that's more than 900 dump trucks) of aquatic invasive plants and fragments from its lagoons.
    • Boat back up station: The boat back-up station is designed to ensure that invasive weeds don't make their way to Lake Tahoe on a boat propeller to propagate and spread.
    • Bubble curtain: In 2018, a bubble curtain was installed across the west channel entrance. Using bubbles to create a barrier, it reduces the potential for movement of fragments into Lake Tahoe.
    • Sea Bins

    TKPOA's current methods:

     

    Bottom Barriers:

    • ​Synthetic mats are installed to block out sunlight and smother aquatic invasive weeds on the floor of the lagoons. These barriers are installed at locations requested by homeowners who volunteer for this program. The Association is allowed a total of five acres of bottom barrier coverage.

    Non-Point Source (NPS) Plan/ Lake Friendly Landscaping

    • As part of the Waste Discharge Requirements (WDRs) issued to TKPOA by the Lahontan Regional Water Quality Control Board, TKPOA created a homeowner education program, Lake Friendly Landscaping, to ensure residents were following the required policies.

    The Lake Friendly Landscaping program summary

    • Prohibits the use of phosphorus-containing fertilizers.
    • Encourages the reduction of lawn irrigation.
    • Conducts “lunch and learn” seminars for landscaping companies to educate them on ways to reduce the release of nutrients and other contaminants into the lagoons.

    TKPOA's proposed methods:

     

    The following methods are currently being tested or evaluated by TKPOA as solutions to our invasive weeds problem:

     

    Floating Islands: This technology uses native wetland plants on a floating matrix. The roots extend into the water providing a very large surface area through which nutrients are absorbed and removed from the water. The islands may also be deployed with fine-bubble aerators to create water circulation to push more water through the root system. The vendor estimates that a 0.5-HP compressor can push enough air through the aerators to move 12.4 million gallons per day. Status: This technology requires securing funding and permitting.

     

    Circulation System Reactivation

     

    EcoSoar: EcoSoar utilizes an all-natural scientific process to both create and inject superoxide anion radicals (SOAR) into the water column and sediment to clean and restore the water body to a natural, healthy state. Status: The EcoSOAR vendor has agreed to provide a 3-month test of their unit along with installation and technical support, at no cost. TKPOA will need to pay for permitting, electricity and monitoring.

     

    Laminar Flow Aeration: Laminar Flow Aeration (LFA) involves bubbling air through several small diffusers on the bottom of the lagoons. The air bubbles cause the water to circulate, increasing the amount of oxygen at the bottom of the lagoons, which in turn facilitates changing the form of some of the nutrients in the sediment and “muck”. This change is intended to make the nutrients less available for the weeds and algae, which should reduce the rate and amount of weed growth in the area of the LFA test. Status: TKPOA is applying for permits from various regulatory agencies to test a technology called Laminar Flow Aeration (LFA). TKPOA has received financial support for this project from The League to Save Lake Tahoe. The test will be conducted in the lagoons adjacent to Christie Drive, north of Venice Drive.

     

    UV Light Treatment: UVC light damages the DNA and cellular structure of the plants, causing them to die. The light energy goes into the plant and essentially sunburns and scars the outer tissue. It also causes a cell fusion and they can no longer reproduce. Status: This method is currently being tested at the Lakeside Marina. Depending on the outcome of the UV light test, this method could also be one of TKPOA’s many tools in their integrative approach to managing the invasive plants.

     

    Well-monitored, localized use of EPA and Cal/EPA approved selective herbicides in specific areas of the lagoon: While TKPOA is committed to the integrative and long-term control of invasive plants, the reality is that the current approved methods are not enough to reduce the infestation to the point where the methods can keep up with the growth across the 170 or so acres that make up the lagoons. Along with other proposed methods outlined earlier, TKPOA is proposing a short-term, highly managed spot use of herbicide in specific areas of the lagoons, away from the main channel and far from the entrance to Lake Tahoe. The aim is to efficiently reduce invasive plant growth to a level where all methods can be integrated effectively and thereby reduce the need for harvesting.


    Further information on the proposed EPA approved herbicides

    • The herbicides would only be used in a series of controlled and careful applications to reduce the volume of plants to a manageable level, and then replaced with other methods for long-term weed management.
    • Target the specific aquatic invasive plant species but do not affect native aquatic plants, fish, wildlife, or recreation.
    • Proposed rate of application would be well below the EPA-approved maximum allowable concentrations and at that application rate is nontoxic to fish, wildlife and humans.
    • Projected to quickly degrade after application and not exit the Tahoe Keys lagoons during those limited application periods.
    • Endorsed by a number of independent national and regional experts including the California Department of Food and Agriculture, UC Davis, US Army Corps of Engineers, University of Nevada, Reno and the California Department of Fish and Wildlife.

    The proposed aquatic herbicide treatment, as outlined in the Tahoe Keys Lagoon Restoration Project proposal, is as follows:

    • Year 1: While continuing to apply all other controls, apply herbicide to 13.7 acres in Tahoe Keys Lagoons and 4.5 acres of Tallac Lagoon to test effectiveness of treatment.
    • Year 2: Apply only other integrative methods (non-herbicide) and evaluate the efficacy of herbicide treatment test.
    • Year 3: While continuing to apply all other controls and based on the learnings of the tests in Year 1 and Year 2, apply herbicide up to 72 acres in Tahoe Keys Lagoons and Tallac Lagoon. (8-15 acres/day for 5-10 day period)
    • Year 4: While continuing to apply all other controls, apply herbicide up to 64 acres in Tahoe Keys Lagoons and Tallac Lagoon. (8-15 acres/day for 5-10 day period)
    • Years 5-12: Apply all other controls. If needed, apply herbicide to maximum of 35 acres in Tahoe Keys Lagoons and Tallac Lagoon, in any one year.

    The project performance criteria for the herbicide use is as follows:

    • Achieve and maintain at least 75% reduction of invasive plant biomass from the baseline.
    • Achieve and maintain a minimum of three feet of vessel hull clearance within navigation channels.
    • Increase native plants in treatment areas from the baseline.
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