Historic fight: Tahoe Keys battles invasive weeds with herbicides

Laney Griffo
TKPOA and partner agencies began application of herbicides on May 25.
Laney Griffo/Tahoe Daily Tribune

SOUTH LAKE TAHOE, Calif. — History was made this week as scientists and agency leaders gathered in the Tahoe Keys at Lake Tahoe to watch the application of herbicides as part of a massive effort to knock back aquatic invasive species.

Herbicides were applied to three sites within the Tahoe Keys on Wednesday, May 25, and will be applied to 10 other sites over the next week. The herbicides, Endothall and Triclopyr, were applied to the restricted boating Area B which encompasses the waterways that are accessed from Venice, Morro and Monterey Drives.

The morning of the application, Tahoe Keys Property Owners Association staff members were out at the access point to Lake Tahoe at 4 a.m. taking flow measurements. They will continue to monitor the water flows throughout the application period.

“The homeowners are really excited to get started on this,” said Dave Peterson, TKPOA board president. “We’ve been trying to manage AIS with harvesting and everyone realizes that’s just not working.”

At the entrance of Area B are double turbidity curtains, as well as a boat barrier. This serves to keep boats away and to keep the herbicides within the designated area.

The herbicides are being distributed by Aquatechnex, a company that specializes in aquatic invasive species management. Their boats are equipped with monitors that allow them to take volume measurements throughout the application process, to ensure they are applying the correct amount.

The herbicides are infused with a red dye so they can see how much is being released. The dye will also allow them to see if the herbicides have moved outside of the application area.

Red dye was added to the herbicide so scientists can track where the herbicide goes.
Laney Griffo/Tahoe Daily Tribune

The sites will be monitored for at least 21 days after the application, where they will be looking for remnants of the dye within the test site and outside of the turbidity curtain.

A boat was following the main boat and a crew with a pump tank was waiting just off shore so that if there was a spill, they could immediately respond and pump it out. The first day of application went smoothly and the emergency pump tank wasn’t needed.

Dr. Lars Anderson, who is the lead scientist on the project, said he expects to be able to see success within 48 hours of application.

“There are several ways to monitor what happens with the plants,” Anderson said. “We actually, physically rake them up from 30 spots at each site. That tells us what species are there and what condition they’re in.”

The health of the plants are rated on a 1 to 5 scale, with five being the healthiest. Anderson said the plants are currently fours and fives but after three to four weeks, he expects them to be ones and twos.

“What this will also tell us, is from now to midsummer are the species changing, are the natives getting more frequent, are they getting better as we’ve gotten rid of the competition,” Anderson said.

In addition to hand raking, they will also be monitoring the plants using a hydro-acoustic scan. The scan tells them where the plants are, how tall and how dense they are.

“It’s a really good way to find out if there has been any effect on the biomass of those,” Anderson said.

The herbicides are just one part of the overall control methods test. Many of the sites that receive herbicides, including the three that were treated on Wednesday, will also be treated with the UV-light boat.

There are 20 sites total receiving some sort of treatment this year. Some sites will be getting just the herbicides, some just UV and some will be getting laminar flow aeration. There are also five control sites.

20 different sites will be getting treatment.

The methods test will be conducted over three years but herbicides will only be applied this year. After, the scientists will be able to see what method or combination of methods helped knock back the invasive species the best.

The first day of herbicide application was emotional for Anderson and the other people who have been working to solve this problem. The CMT has been in the works since 2017 but the Tahoe Keys have been experiencing invasive species since the 1980s.

“This is a huge milestone for Lake Tahoe in terms of aquatic invasive species and our understanding. There’s been a huge collaborative partnership that’s come together in order to get us to this point and the results of this project are going to help determine weed management in the Keys moving long into the future,” said TPRA Community Engagement Manager Victoria Ortiz.

“We always make our decisions on sound science and this project is based on science. The lake will be safe and ultimately we’re working towards keeping Tahoe blue by addressing one of the biggest threats facing the lake which is aquatic invasive species,” Goodman Collins said.

While most people are in agreement that the weed issue needs to be solved, the application of herbicides was contentious.

TKPOA and their partners had to get special permission from the Lahontan Water Board for the one-time application. Representatives from the water board were present for the application of the herbicides.

Rick Lind, owner of Sierra Ecosystem Associates, who helped craft the CMT, said the herbicides of today are very different from the herbicides from the 1970s and 80s. They are now targeted, so they don’t have the devastating impact on the surrounding wildlife as they used to.

Still, people worry that this will open the door to indiscriminate use of herbicides.

The League to Save Lake Tahoe was a supporting partner on the CMT and Darcie Goodman Collins, CEO of The League was also present on Wednesday.

Representatives from TKPOA, The League, TRPA and the Lahontan Water Board gathered to watch the herbicide application.
Laney Griffo/Tahoe Daily Tribune

“It’s a very exciting day, working for the League to Save Lake Tahoe, our goal is always to work towards keeping Tahoe blue and that’s exactly what this control methods test is doing,” Goodman Collins said. “We always make our decisions on sound science and this project is based on science. The lake will be safe and ultimately we’re working towards keeping Tahoe blue by addressing one of the biggest threats facing the lake which is aquatic invasive species.”

The use of herbicides is not taken lightly by anyone involved in the project but the overall mood of the day was excitement that the community is taking a big step forward in addressing the weed issue.

Invasive weeds have been present in the Keys since the 1980s.
Laney Griffo/Tahoe Daily Tribune

To stay up-to-date on the project, visit

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