You’ve heard it before: aquatic invasive species are the greatest ecological threat to Lake Tahoe’s water quality and clarity. They outcompete native species, affect nutrient cycling, and impact algal growth, which can turn Lake Tahoe’s beautiful blue water green.

Nowhere is that threat more visible than in the warm, shallow lagoons of the Tahoe Keys, where invasive plants clog the water. Fragments of those plants regularly break off and float away – carried by currents, watercraft, and people – to other parts of the Lake, where they can resprout and start new infestations.

After decades fighting the growing weed problem, the Tahoe Keys Property Owners Association worked with the Tahoe Regional Planning Agency, League to Save Lake Tahoe, and other partners to develop the Tahoe Keys Control Methods Test project. This comprehensive test of methods will help determine how best to reduce and control invasive plants in the lagoons and prevent the infestation from spreading further into the Lake.

This fall, the TKPOA completed the second year of the three-year CMT. In the first year, they significantly reduced plant biomass using an array of methods, including the one-time, targeted use of herbicides in select areas blocked off behind double walls of barrier curtains. The goal of year two tests was to maintain the year one weed reduction, or “knock-back,” using entirely non-chemical methods, such as UV light treatment and diver-assisted suction dredging.

A report detailing what happened and preliminary results from the year two is available for you at tahoekeysweeds.org. With hundreds of thousands of scientific monitoring data points to analyze, and extremely variable environmental conditions to factor in (like much colder, deeper water compared to year one), the outcomes are still being determined. Generally, we’re seeing that the initial knock-back in invasive plant density was largely sustained during year two. A more detailed report will be released in the spring of 2024. Once completed, the three-year CMT will inform a long-term approach for sustained invasive weed management in the future.

For everyone who enjoys Tahoe, aquatic invasive species should be on your mind anytime you plan to get on the water. The League and TRPA are helping monitor and manage this important test because we, like you, support solutions that protect our Lake.