The amount of hydrogen ions in the water, i.e., the pH, is a very critical characteristic determining whether zebra mussels will be able to survive and reproduce in a water body. Sprung (1987) indicated that a pH lower than 7.4 inhibited zebra mussel larval development. Kornobis (1977) reported that pH levels of 7.2-8.7 had little effect on veliger densities. Stanczykowska (1977) recorded zebra mussels in European lakes with pH levels of 7.7-8.5. Laboratory studies by Bowman and Bailey (1998) have indicated that the upper pH tolerance limit of zebra mussels is between 9.3 and 9.6.