These mussels have a hard time going from veligers to adults due to environmental factors such as low calcium concentrations in our mtn lakes.
The CDOW will say their efforts largely keep these particular species from spreading. That's not exactly 100% true. Their efforts can help but environmental factors help keep them from spreading much more.
The below is a thesis written by a CU master's student. She cites studies by Drake & Bossenbroek, 2004, among others, conducted to prove that Dreissena have an extremely low likelihood of taking hold in Rocky mtn waters. Colorado's east plains reservoirs are more suitable for veligers to mature to adulthood but still not as suitable as midwestern and eastern lakes.
The extremely detailed thesis about the economic impact of prevention vs eradication(treatment) is found here: [log in for link]
One paragraph that quickly sums up the studies' details: Environmental Factors Affecting Mussel Spread
Levels of calcium, pH, alkalinity, temperature, dissolved oxygen, Secchi depth, nutrients, and available substrate have all been found to be important predictors of dreissena habitat suitability (Ramcharan et al., 1992 Mellina & Rasmussen, 1994 Cohen & Weinstein, 2001 Drake & Bossenbroek, 2004 Whittier et al., 2008 Claudi & Prescott, 2009). Several studies address the possible spread of dreissena based solely on environmental factors.
In 2004, Drake and Bossenbroek developed a model to predict the potential distribution of zebra mussels in the United States using biological and geological variables including average annual temperature, bedrock geology, elevation, flow accumulation, frost frequency, max and min temperatures, precipitation, slope, solar radiation, and surface geology. Of particular interest to this study are Drake and Bossenbroek's predictions for the Rocky Mountain region. Two of the three models developed by Drake and Bossenbroek (2004) predict that zebra mussels will not spread to the Rocky Mountain region. The third model, which includes all of the listed variables with the exception of the elevation variable, predicts the Eastern Plains of Colorado to be at high risk of mussel infestation, but still predicts the mountainous regions of the state to have very low probabilities of infestation. At the time these models were developed, the third model was deemed the least reliable of the three, and the consensus was that the Rocky Mountain States were very unlikely candidates for mussel infestation.
Whittier et al. (2008 ) use calcium concentrations to assess the risk of dreissena invasions for ecoregions across the contiguous U.S. Using calcium concentration data from over 3000 stream and river sites across the nation, they define risk of dreissena invasion based on calcium concentration. Ecoregions with average calcium concentrations below 12 mg/L are defined as very low risk, 12-20 mg/L as low risk, 20-28 mg/L as moderate risk, and greater than 28 mg/L as high risk. In their assessment, the Eastern Plains of Colorado have a high risk of dreissena invasion based on calcium concentration, and the risks to the mountainous regions of the state are highly variable.