The calcium level of a water body is a very critical characteristic for zebra mussel population establishment. Zebra mussels do not survive when there is low calcium concentration in the water, since calcium is an essential element in the composition of the bivalve shell. Sprung (1987) reported that 40-55 mg/liter was sufficient for larval development and that a minimum of 24 mg/liter was necessary for 10 percent larval survival. Stanczykowska (1977) recorded calcium levels of 28-109 mg/liter in lakes with successful zebra mussel populations. Calcium concentrations of 15 mg/liter or less were found to limit the distribution of zebra mussels in the St. Lawrence River (Mellina and Rasmussen 1994). Hincks and Mackie (1997) reported negative shell growth at calcium levels less than 8.5 mg/liter.