1) Quashing Quagga: Fate and Effects to the Benthic Community of a Copper Treatment to Eradicate Invasive Mussels in a Large Western River – Presenter: Austin Baldwin, U.S. Geological Survey

Copper-based chemical treatments are commonly used to eradicate invasive mussels in small ponds and lakes, but their use in large rivers has been limited. In 2023, in response to a detection of invasive quagga mussels, a 10-kilometer reach of the Snake River (Idaho, USA), was treated with an unprecedented 19,300 kg of chelated copper molluscicide to a target concentration of 1,000 µg/L for 10 days. We assessed the transport and fate of the copper, its accumulation in sediments, and its exposure and effects on the non-target benthic community downstream. Findings from this study can help watershed managers plan future invasive mussel responses while protecting culturally, economically, and ecologically important non-target species in large rivers.

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2) Challenges of Eradication Efforts for Zebra Mussels in Highline Lake, Colorado, using EarthTec QZ – Presenters: Tawni Firestone & Robert Walters Colorado Parks and Wildlife

Following the detection of an isolated population of zebra mussels in Highline Lake, Colorado, in 2022, an eradication effort was initiated in spring 2023. The reservoir was lowered by approximately 9.1 meters and EarthTec® QZ, a copper-based EPA-registered molluscicide, was applied at 4 ppm (240 μg L-1 copper). Water samples were collected prior to, during, and following the treatment to monitor copper concentrations and water quality parameters. An average 148.95 ± 43.46 μg L-1 dissolved copper concentrations was observed across all treatments, with variations influenced by depth and timing of application. Sufficient copper distribution was achieved throughout the reservoir, as confirmed by water sample analysis and geostatistical modeling. However, suboptimal water temperatures (below 7 °C for extended periods) were maintained during the treatment. The continued presence of veligers and adult mussels in late summer 2023 was revealed by post-treatment monitoring, indicating an unsuccessful eradication attempt. A subsequent, more intensive retreatment in fall 2023 was completed and involved higher EarthTec QZ concentrations (8 ppm; 480 μg L-1 copper) prior to complete draining of the reservoir. Average copper concentrations were 384.79 ± 38.62 μg L-1 and slightly higher temperatures than the first treatment were observed (8.87 ± 0.98 °C). The second treatment demonstrated more effectiveness, as no living zebra mussel or veliger detections were observed in the reservoir in 2024. The reservoir was then drained to allow for complete freezing and desiccation of any remaining mus sels over the winter 2024. While no live zebra mussels were detected within the reservoir post-draining, two veliger detections were recently confirmed following the refilling of Highline Lake in 2025, with reinfestation likely occurring via the Colorado River during this process. The challenges of zebra mussel eradication, particularly the importance of optimizing treatment timing with respect to water temperature, copper bioavailability, and site location are highlighted in our study.

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4) Managing the Unmanageable: Preparing for the First Whole-Lake Copper Treatment for Zebra Mussels in Minnesota – Presenter: Olivia Nyffeler, The University of Minnesota’s Aquatic Invasive Species Research Center

Zebra mussels (Dreissena polymorpha) have spread to nearly 380 lakes across Minnesota and once established, are difficult to remove. Prevention remains the primary strategy due to its cost-effectiveness and ability to limit spread; however, once a lake becomes infested, effective management options are limited. Previous work has evaluated low-dose copper treatments at large spatial scales with promising results. Applications in bays of Lake Minnetonka (MN) have demonstrated reductions in zebra mussel settlement and veliger densities while minimizing impacts to native mussels and other non-target communities. Building on these findings, Lake Riley, a 296-acre mesotrophic lake in Eden Prairie/Chanhassen, MN, was selected for Minnesota’s first whole-lake low-dose copper treatment using EarthTec QZ. This project integrates whole-lake treatment with comprehensive ecosystem monitoring and coordination among state, federal, and local partners. This presentation will describe treatment implementation, monitoring design, and early insights, and will discuss how results from this effort can inform the development of a real-world framework for managing established zebra mussel populations and restoring ecosystem function.