Tahoe Keys Weeds

Lake Tahoe is threatened by invasive aquatic weeds and a new proposal to control the weeds with chemical pesticides. Your help is needed to save it. 

Tahoe Keys is a private residential development of over 1500 homes and a marina at the south end of Lake Tahoe, built in the 1960s by dredging and destroying the western half of the Upper Truckee Marsh. Over the past several decades, the largely stagnant Keys lagoons have become infested with non-native aquatic plants, and the continued expansion of this infestation endangers the ecology of the lake. Various measures have been applied over the years to reduce the infestation, with limited effectiveness. The Tahoe Keys Property Owners Association (TKPOA) now proposes to test the application of herbicides to control the infestation. The Sierra Club Tahoe Area Group is committed to protecting the purity of Lake Tahoe, and is opposed to any and all use of herbicides in the Keys and any other waters that connect to the lake.



Tahoe Keys was built in the 1960s at the south end of Lake Tahoe by dredging the western half of the Upper Truckee Marsh.  Its construction destroyed that portion of the marsh, which served as a major filter for water entering the lake as well as habitat for fish, birds, and other wildlife. Environmentalists consider the Tahoe Keys to be one of the most appalling environmental atrocities ever committed upon Lake Tahoe. 

In the 1980s and 1990s, the invasive weed Eurasian watermilfoil (Myriophyllum spicatum) became established in the Tahoe Keys lagoons.  Another non-native species, Curly-leaf pondweed (Potamogeton crispus), was first discovered in Lake Tahoe in 2003.  The two invasive, non-native aquatic weed populations in the Tahoe Keys lagoons have been growing rapidly. In recent years, 85% to 90% of the available wetted surface in the lagoons has been infested with aquatic weeds, mostly these two non-native invasive species. 

Seasonal harvesting has been the main weed control practice in the Tahoe Keys lagoons since the mid- 1980s. Continual harvesting throughout the summer months keeps the lagoons navigable, but reductions in aquatic weed biomass are temporary.   Bottom barriers (mats) have also been used, with limited results. A three-year test of a 6-acre laminar flow aeration installation began operation in April 2019. 

Efforts have also been made to limit migration of invasive weeds to the Lake.  These efforts have included the installation of a “bubble curtain” at the entrance to the lagoons to intercept floating plant fragments, skimmers to catch floating fragments pushed back by the curtain, and a station at the Lake entrance where boats are backed up to dislodge plant fragments before entering Lake Tahoe.  While these methods have shown some promise and have been effective in controlling smaller infestations elsewhere in the lake, the overall infestation of the Keys has continued to get worse over time.  

Both the federal government and California have designated Lake Tahoe as a Tier 3 “Outstanding National Resource Water”.    The Clean Water Act requires that the water quality of Tier 3 waters must be maintained and protected without exception, meaning that Tier 3 waters must not be allowed to be degraded. As such, any degradation, such as the use of herbicides, requires an Anti-Degradation Analysis that meets both Federal and California regulations.


Tahoe Keys Aquatic Weed Control Methods Test

In 2019, the Tahoe Keys Property Owners Association (TKPOA) proposed a two-year project to test large-scale control methods, with emphasis on aquatic herbicides - the “Tahoe Keys Aquatic Weed Control Methods Test” (CMT).

The two public agencies (“Lead Agencies”) required to approve and monitor such a test are the Tahoe Regional Planning Agency (TRPA) and the Lahontan Regional Water Quality Control Board.   In particular, the use of herbicides requires an exemption from Lahontan Basin Plan prohibition of use of aquatic pesticides in Lake Tahoe, as well as TRPA approval of testing aquatic herbicides as a potential aquatic invasive species control tool. 

On July 6, 2020, the Lead Agencies released a Draft Environmental Impact Statement and Environmental Impact Report (DEIS/DEIR) for the CMT project. 

  • The “Proposed Project” in the DEIS/DEIR would test the use of aquatic herbicides in the Keys lagoons that flow directly to Lake Tahoe along with non-herbicidal treatment.  The project includes a set of 21 small-area tests in the Keys of two aquatic herbicide products, ultraviolet light treatment, and laminar flow aeration, each tested alone and in combination.
  • "Action Alternative 1" (AA1) would test only non-herbicidal methods of aquatic weed control.  
  • "Action Alternative 2" (AA2) would dredge the organic material and sediment on the bottom of the lagoons to remove the roots and turions (buds) of aquatic weeds at three test sites in the Tahoe Keys lagoons, then replace the dredged material with a layer of coarser sand and gravel. 

Sierra Club supported AA1, which was also identified by the DEIS/DEIR as the environmentally superior alternative.  


Lahontan Water Board Approval and TAG Response

On January 13, 2022, the Lahontan Water Board adopted a set of Resolutions and Orders certifying the Joint Environmental Impact Report/Environmental Impact Statement (Joint EIR/EIS) for the Project, a Resolution granting an exemption to a waste discharge prohibition for aquatic pesticide discharges to surface waters prescribed in the Water Quality Control Plan for the Lahontan Region (Basin Plan), a National Pollutant Discharge Elimination System (NPDES) Permit for the discharge of aquatic pesticide residues, rhodamine dye, and lanthanum-modified clay, and an Order establishing a Mitigation Monitoring and Reporting Program to monitor mitigation measure implementation identified in the Joint EIR/EIS.

Sierra Club Tahoe Area Group We filed an appeal to the State Water Board after Lahontan issued the permit but they have not responded and in the meantime herbicides were released in May.  After requesting information from Lahontan (since very little is being disclosed to the public), we have found out that the herbicide releases have caused the water quality to be degraded in the receiving water by exceeding the limits in the permit at more than one location. We will continue to request information and will be proceeding with our next move soon. Regulations require showing that non-chemical means are ineffective before other means are used, and this was clearly not the case. We believe that this “testing” is opening the door for ongoing herbicide use in the lake. In the meantime, boating is continuing in non-testing areas of the Keys and is spreading noxious weeds throughout Lake Tahoe. We continue to monitor the project and aim to hold officials accountable.


Tahoe Area Sierra Club Concerns about the Control Methods Test

Here are reasons why the Sierra Club strongly opposed the Control Methods Test and continue to oppose the ongoing project:

  1. The Keys’ lagoons are hydrologically connected to Lake Tahoe, which is designated by the EPA to be a Tier 3, Outstanding National Resource Water (ONRW), referring to the adoption of the ONRW language in 40 CFR 131.12. This means its high water quality must be protected and maintained according to State and Federal anti-degradation regulations. In addition, Lahontan’s own Basin Plan requires that failure of all non-chemical methods must be demonstrated prior to authorizing the use of herbicides. TKPOA has not sufficiently tested non-herbicidal treatment methods, and it certainly has not met this prohibition exemption requirement of demonstrating the ineffectiveness of non-herbicide treatment methods, but instead continues pursuing herbicide use.
  2. Applying aquatic herbicides is like applying a Band-Aid to a severed artery.  The use of herbicides does not address the causes of the problem: decades of nutrient buildup from the heavily fertilized lawns in the Tahoe Keys, the numerous stormwater outfalls into the lagoons, and nutrient recycling from dead and dying weeds. Herbicides or not, weeds will continue to flourish under these conditions until the conditions supporting the infestations are removed.
  3. Experience in other lakes throughout the country indicates that aquatic herbicides require repeated applications because the herbicides fail to completely kill the weeds, particularly their seeds and roots. Thus, herbicide application would be required in perpetuity, and would inevitably lead to herbicide use throughout the lake. By allowing the agencies the opportunity to overcome the non-degradation regulatory hurdles, the Proposed Project, if it is allowed, would be “a foot in the door” for herbicide use throughout the lake with no time limits established.
  4. The Lead Agencies assert that the aquatic herbicides are safe because they have been approved by the EPA. However, the EPA has long asserted that Roundup and other pesticides are safe.  Would you want Roundup poured into Lake Tahoe?
  5. The Proposed Project does not explore the full range of options, only aquatic herbicides and a few non-chemical methods. If we want to rid Lake Tahoe of weeds, we must expand our options.
  6. The Proposed Project only proposes to reduce the height of the invasive weeds by about 3 feet from the surface to provide weed-free navigation for boat travel. It never proposes to solve the problem of perpetual weed growth.
  7. Dredging the organic material and sediments, proposed by AA2, is not a realistic option because aluminum sulfate was dumped in the lagoons to settle the suspended sediments when the lagoons were built. Aluminum sulfate is extremely toxic to fish and other organisms in Lake Tahoe. Therefore, both the Proposed Project and AA2 propose control methods that would release toxic substances into lake water and should be strongly opposed.


The Only Long-term Solution is to Restore the Wetland

Returning the keys lagoons to a healthy functioning wetland would solve the weed problem by eliminating the weed’s habitat. It would eliminate the need for herbicides. The wetland would filter nutrients and pollution from Tahoe, immediately improving the water quality and clarity of our cherished Lake Tahoe. Done well, it could enhance the Tahoe Basin's health, beauty and quality of life, while preserving property values.

In addition to reducing the growth and spread of the weeds through non-chemical methods, the Lead Agencies should begin addressing the long-term problem by restoring some or all of the lagoons to marsh habitat.

In Sierra Club’s comments to the NOP, we requested this option be considered and thoroughly examined in the DEIS/DEIR, but it was rejected because it “didn’t meet the goals and objectives” of the project, which was to "test" various control methods.

What is more important? Managing the weeds for the convenience of boaters, or protecting Lake Tahoe's world-famous clarity, majestic color, and purity?

The time has come for the past destruction of marsh habitat to be healed. The time has come to restore a natural marsh, thereby permanently eliminating the invasive weeds, burying the years of nutrient buildup in the Keys, and providing filtration for new sources of nutrients and other pollutants into the Keys. Restoring to marsh some or all of the stagnant lagoons would also provide natural habitat for birds and other wildlife and could be done in a way to increase property values, beauty and quality of life. In the meantime, the Keys should test only with non-chemical methods as proposed in AA1.