Nine thermal springs, in three groups, occur along the flank of Sulphur Mountain in Banff National Park. The principal recharge zone is suggested to be above 2000 m elevation on Mount Rundle, circulation depths are estimated to be 3.2 ± 0.6 km, and discharge is focused along the Sulphur Mountain Thrust. Springs show constant temperature and total dissolved solids load throughout the winter, whereas both drop in association with spring snowmelt. The degree and timing of temperature drops are a function of elevation, with the highest springs showing the earliest and most significant temperature drop. The highest elevation springs also show the greatest seasonal variability in water chemistry. Unusual seasonal flow stoppages of these springs are related to extreme low precipitation years. The biogeochemistry of the thermal springs and population fluctuations of the endemic and endangered Banff springs snail (Physella johnsoni) are strongly related to seasonal variability in flow rates. Changes in redox conditions associated with an influx of shallow groundwater during spring snowmelt negatively impact the microbial community that forms a principal food supply for the snail.