Initial results of herbicide use in Tahoe Keys promising |

Initial results of herbicide use in Tahoe Keys promising

SOUTH LAKE TAHOE, Calif. — Initial observations of the Tahoe Keys Aquatic Invasive Species Controls Method Test shows promise but the test is far from over. 

The first of a three year methods test is two months underway and scientists are already seeing promising results. 

The CMT is testing several different methods to knock-back aquatic invasive species over the next three years. Applications of herbicides began on May 25 and wrapped up on May 31, the same day UV light treatments began. 

“Initial observations are encouraging,” said Dr. Lars Anderson, lead scientist. 

There were two different herbicides that were applied and Anderson said so far, they’ve seen a reduction of target plants and minimal effects on native species. 

As per the permit conditions, extensive monitoring has been ongoing since the start of the test. 

A sample of the aquatic invasive species 14 days after herbicide application. The brown is the AIS, while the green plants are native.

During a presentation to the Tahoe Regional Planning Agency Governing Board, Aquatic Resources Program Manager Dennis Zabaglo said the large wind events at the end of May did cause a trace amount of herbicides to be detected on the wrong side of the turbidity curtains, which were set up where herbicide testing was taking place. 

The contingency plan was immediately put in action, including Tahoe Keys Property Owners Association divers diving down to repair the curtain. 

Additional monitoring took place at multiple locations closer to the channel and lake and no additional herbicides were detected. 

“Our plan worked as we intended it to and nothing got close to reaching the lake,” Zabaglo told the board. 

Waterways have been closed to Tahoe Keys homeowners during the test, and while they were scheduled to reopen in late-July, the reopening date has been delayed until Aug. 19. 

“The levels of herbicides are taking longer than expected to become undetected,” Anderson said, leading to the closures to be extended. 

However, he said the levels are getting lower so things are looking promising. 

The UV light testing will continue, likely into October. Following the completion of the first year of testing, Anderson is excited about the amount of data they will have available. 

The herbicides are only being applied the first year, so no more herbicides will be applied during the remaining two years of the test. 

The League to Save Lake Tahoe, who is one of the sponsors of the test, has been keeping an eye on progress of the test as well. 

“Much has been accomplished in the Tahoe Keys Control Methods test in a short amount of time,” said Jesse Patterson from the League, who has been deeply involved in controlling aquatic weeds in the Tahoe Keys for the past decade. “There have been bumps in the road, but that’s to be expected with any test. Each challenge is an opportunity to learn and improve, so the long-term plan to control aquatic invasive weeds in Tahoe is the best it can be. The League will stay engaged through the test’s three-year timeline.”

To keep track of progress of the test, visit

Correction: This article has been updated to say that a trace amount of herbicides was detected on the wrong side of the turbidity curtain, not the bubble curtain.

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