This report describes the use of the acid-stabilized ionic copper formulation called EarthTec QZ to treat an entire lake heavily infested with quagga mussels for the purpose of eradicating the invasive species. This is the first recorded instance of a lake-wide eradication effort of quagga mussels and is also the largest and deepest lake known to have been the subject of an effort to completely eradicate either quagga or zebra mussels.