Tahoe Keys Lagoon Aquatic Weed Control Methods Test (CMT) Monitoring Program

Aquatic invasive weeds have overtaken the Tahoe Keys lagoons and are spreading into Lake Tahoe where they threaten the water quality and aquatic ecology of this treasured high-mountain lake. In addition to evaluating traditional and innovative approaches to managing invasive aquatic weeds, the CMT Monitoring Program further evaluates the impacts of various treatments on water quality and response of the aquatic plant and benthic macroinvertebrate (BMI) communities.

ESA has been working for the Tahoe Regional Planning Association (TRPA) on the aquatic weed control problem for more than five years. Beginning with an expanded checklist for the CEQA and TRPA environmental review processes, and continuing through the Final EIR/EIS, ESA led the evaluation of weed control alternatives on aquatic resources (i.e., water quality, limnology, fisheries, and aquatic ecology). Currently ESA is working closely with our subconsultant, Marine Taxonomic Services (MTS), to provide comprehensive monitoring at 24 sites in the Tahoe Keys Lagoons that has, or currently includes:

• Weekly sampling for nutrients in the water that could contribute to a harmful algae bloom (HAB) due to cyanobacteria
• Bi-weekly sampling for macrophyte species abundance and health
• Annual assessments of the BMI community
• Grab sampling for cyanobacteria speciation and subsequent cyanotoxin analysis
• Following the identification of New Zealand mudsnails in Lake Tahoe, the ESA and MTS team monitor for this new invader in the Tahoe Keys

The Tahoe Keys CMT marks the very first application of EPA-approved aquatic herbicides in the Tahoe Basin to evaluate future operational use to combat invasive aquatic plants. ESA was instrumental in completing the Environmental Impact Statement/Environmental Impact Report (EIS/EIR) in 2019 that informed permitting decisions for this work.