The East Kootenay Invasive Species Council (EKISC) conducts invasive mussel monitoring on various waterbodies across the region. A water sample is taken at each lake using a plankton tow net to test for invasive Zebra and Quagga mussel larva. Ancillary data including temperature, pH, and Secchi depth are taken at each water body and are shared in this dataset. Higher priority lakes (i.e., lakes that receive more transient use) are sampled twice per month, while lower priority lakes are sampled once per month from the beginning of June until the end of September. This dataset contains ancillary data collected from St. Mary Lake.