Regarding the presence for quagga and/or zebra mussels, Utah Division of Wildlife Resources' classification system follows:
If an affected water body evidences no detections of quagga or zebra mussel life forms for an extended period of time (time varies based on classification), declassification may be considered at the end of the last assessment year, once all samples are analyzed; the year of discovery is the zero year. The mere passing of time with no detections for quagga or zebra mussel life forms is not a guarantee for declassification to occur. Natural resource managers are perpetually gaining experience and knowledge, all of which could affect the declassification process. Fortunately, it is not uncommon for aquatic animal transfers to require several introductions before a successful, self-sustaining population is established. So, aggressive containment management (inspect arriving boats, provide professional decontamination for departing boats, and market self-decontamination via Clean, Drain & Dry) at Utah's water bodies may result in fewer or no introductions causing initial introductions to fail.
Declassification to "not detected" for a quagga or zebra mussel affected water must follow an extended period of intensive sampling as follows:
See full definitions in Rule R657-60, Aquatic Invasive Species Interdiction.