Animal programs

“A Different Animal”: Herbicides Proposed to Control Invasive Tahoe Keys Weeds

SOUTH LAKE TAHOE, Calif .– For more than a decade, eliminating invasive aquatic weeds in the Tahoe Keys has been a priority for the Tahoe Keys Property Owners Association, the League to Save Lake Tahoe, the Tahoe Regional Planning Agency and others.

The Tahoe Keys is a residential development that consists of approximately 1,500 homes and approximately 170 acres of waterways connecting to Lake Tahoe.

Since the 1980s Eurasian Watermilfoil has been widespread in the Keys. In 2003, the curly pondweed was also discovered there and continued to grow.

According to Dennis Zabaglo, director of the aquatic resources program at TRPA, in 2014, the curly-leaved pondweed represented 10% of the samples taken. In 2021, it overtook watermilfoil and now represents 55% of samples taken.

The Tahoe Keys are a favorite place for aquatic invasive species to thrive, as the waterways are warm, stagnant, and shallow. At the height of summer, AIS is present in nearly 100% of rivers.

“The Tahoe Keys are one of the greatest ecological threats to Lake Tahoe, its zero point for invasive aquatic weeds, its spread to the lake, there is a lot of boating activity, there have been blooms of dangerous algae in the Keys since 2017, the water quality is bad, it’s a big problem, “said Jesse Patterson, SU strategy director.” You have to go to the Keys if you want to solve the problem. problem for the whole lake. ”

A 2013 agreement between TKPOA and the Lahontan Regional Water Quality Control Board requires the Keys to tackle the weed problem in exchange for their permission to dig lagoons navigation channels into the lake. Although they have tried several solutions over the years, the problem has only grown.

To find long-term solutions, TKPOA has partnered with Lahontan, TRPA, The League as well as the Tahoe Water Suppliers Association and the Tahoe Resource Conservation District. They have developed a test of control methods, which is a 3-year program. In the first year, methods would be implemented to dramatically reduce the prevalence of weeds, and years two and three would be maintenance methods to keep weeds away.


One such solution offered by the TKPOA are herbicides, which have never been used before in Lake Tahoe. The use of herbicides is controversial to say the least and is not a decision agencies take lightly.

“We are dealing with a different animal,” Zabaglo said during a presentation to the APTR board of directors. “This test is an opportunity to balance the fine line or the urgency with getting it right.”

CMT suggests the use of herbicides only once in the first year. In addition, a third-party environmental impact consultant was engaged to examine the potential unintended consequences of herbicide use.

“We are also very concerned about the use of herbicides,” Patterson said. “Previous versions of the proposal had a more aggressive use of herbicides, we were actually not in favor of… but having said that, we need to know if they have a role to play in the larger system.”

Jim Good of Environmental Science Associates was on the oversight committee and they recommended several protective measures be put in place.

Herbicides will be applied at a rate well below the rates approved on the label. In addition, anyone working with herbicides should be trained and licensed. Finally, there will be a spill prevention and response plan and an accelerated aeration plan to dissolve the herbicides if they find they are not working.

The Sierra Club Tahoe Area Group has been the biggest opponent of the use of herbicides. During the presentation to the board, Tobi Tyler, a former member of the Toiyabe branch committee and the Tahoe area group, said there would be no way to use herbicides once and that this would open the floodgates to other areas of the lake being treated. with herbicides.

“Applying aquatic herbicides is like applying a bandage to a severed artery. Herbicide use does not address the root causes: decades of nutrient build-up from heavily fertilized lawns in the Tahoe Keys, numerous stormwater discharges into lagoons, and recycling of nutrients from weeds. dead and dying, ”Tyler wrote in a blog post. post about the problem. “Herbicide or not, weeds will continue to thrive under these conditions until conditions favoring infestations are removed. “

However, Patterson countered that if CMT is approved, it will be for a one-time herbicide use, so if they wanted to use more, the group would have to seek additional approval.

At the APTR board meeting on Wednesday, board member Hayley Williamson shared a personal anecdote about the lake she grew up on in the Midwest.

The lake had been invaded by watermilfoil and herbicides were used to successfully control the weeds.

“The herbicides saved the lake I grew up on,” said Williamson.

Herbicides are not the only solution proposed in the CMT and it is hoped that the other solutions will complement the use of herbicides after the first year.

Other solutions

The CMT also offers the use of laminar flow aeration and ultraviolet light for the first year.

Pilot programs for the use of UV light have already had some success. UV light is lowered into the water and attacks and kills plants at the cellular level.

It is not selective and also kills native species, but if the invasive species are gone, native species have the opportunity to grow back.

Laminar flow aeration circulates air through several diffusers at the bottom of the lagoons, which circulate the water, increasing the amount of oxygen at the bottom of the lagoons.

The League oversaw testing of this method and Patterson said they had been successful.

The goal after the first year is to reduce weeds by 75%.

Years two and three would continue the progress made on the issues.

Bubble curtains have been installed to prevent weed fragments from escaping into the lake and the use of UV light will continue. Bottom barriers will also be installed to block light from shallow areas of the lagoons and divers will hand pull any weeds that emerge.

It is important to keep in mind that testing control methods is only a test. After three years, successful or not, the group will have to go through the approval process to continue using these methods or to introduce new methods.

One thing Patterson hopes will come out of this test is the possibility that other groups across the country can watch this test and learn.

“Hopefully we’ll learn something that works for Tahoe of course, but if it doesn’t, it’s something that we can export to places whether it works or not to show people what it is. ‘there’s a way to use herbicides that’s not the way we use now because I think there are way too many chemicals in the world and we rely on them too much, “Patterson said .

The Lahontan Water Board will meet on January 12 and 13, during which test approval will be considered. If approved, testing will begin in spring 2022.