Giardia lamblia is a waterborne parasite that causes giardiasis, a diarrheal disease commonly called ""beaver fever”. Despite the comprehensive water quality management measures in B.C., this parasite is often detected in surface water supplies and is the second leading cause of gastrointestinal illness in the province. While current surveillance methods for G.lamblia in water supplies allows for enumeration of the parasite in water, the test cannot differentiate between infectious and non-infectious strains. Natalie Prystajecky is examining a library of archived water samples collected across B.C. over 13 years to determine if the strains in B.C. surface water are infectious to humans and how frequently, what the sources are, and where these strains are found. She is also assessing the effectiveness of control measures such as watershed protection and agricultural waste management best practices in protecting water quality. This information could lead to more effective environmental and health policies and public health interventions.