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, 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 inoculations 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 inoculations causing initial inoculations to fail.
Declassification for a Quagga or Zebra mussel affected water must proceed in a descending step-wise order of management from infested to detected to inconclusive to not detected as follows:
1 Sand Hollow Reservoir, currently classified as "infested," evidenced a single adult quagga mussel living on the bottom side of a boat dock in May 2010; the mussel was removed and the reservoir declared "infested" by the Utah Wildlife Board in June 2010. Prior to the initial discovery, and since that time, no further evidence has been discovered to show the presence of a surviving population of quagga mussels, in spite of intensive sampling (plankton tow nets, beach and underwater searches). However, the analysis of monthly plankton samples following discovery through 2012 has showed evidence of quagga mussel DNA, equating to an inconclusive discovery, although not supported by microscopy. Sand Hollow Reservoir continues to be managed as an infested water body.
2 Red Fleet Reservoir and Electric Lake, where quagga and zebra mussel veligers were respectively discovered in 2008, have now been declassified from "detected" to "inconclusive," since no further evidence for presence of invasive mussels has been measured for three years since discovery. Both waters will be managed in the inconclusive status for at least the 2012 and 2013 boating seasons, as long as survey results continue to not detect quagga or zebra mussels.
3 Huntington North Reservoir (inconclusive discovery in 2008), Joes Valley Reservoir (inconclusive discovery in 2008), Lake Powell (inconclusive discovery in 2007), Midview Reservoir (inconclusive discovery in 2008) and Pelican Lake (inconclusive discovery in 2008), possibly evidenced quagga or zebra mussel veligers. All have now been declassified to "not detected," following monitoring for more than two consecutive years, showing no further evidence of a surviving invasive mussel population.
4 Plankton sampling at Lake Powell produced inconclusive results in 2007 regarding presence for Dreissena veligers. However, after three years with no Dreissena mussel detections (adult, juveniles nor veligers or eDNA), Lake Powell's classification was lowered from "inconclusive" in late 2010 to "not detected." Unfortunately, plankton samples from the Glen Canyon Dam's Penstocks in the spring and summer of 2012 again showed "inconclusive" evidence for quagga mussels--positive polymerase chain reaction assays showing quagga mussel eDNA, and molecular sequencing also identifying quagga mussel. Although microscopic identification could not make a veliger detection. Then, further tests in late summer and fall showed more eDNA and eventually microscopic veligers were detected using cross-polarized light microscopy. All of the 2012 discoveries were made in the lower four miles of the lake between Antelope Point and the dam. It is unlikely that the 2012 discoveries of quagga mussel veligers and their DNA in Lake Powell are related to the earlier discoveries in 2007; the 2012 discoveries represent a new occurrence, and they equate to a "detected" level discovery.