Algae blooms are a prevalent and expanding issue throughout Southern Ontario, primarily because of agricultural activity where fertilizers add excess nutrients (phosphorus and nitrogen) to surrounding soil and water. The Lorraine Bay of Lake Erie in Port Colborne is no exception, as many drainage channels that empty into Lorraine Bay experience severe algae blooms due to the slow-moving water and agricultural runoff. A better understanding of nutrient dynamics in this region is needed to identify where and when to implement mitigation strategies. The research is the first of a two-part series where we aim to understand how nutrients and contaminants are transported and how these solutes are related to major water sources in an agriculturally dominated watershed in the Niagara region. To obtain water source information, a pressure transducer took continuous water level measurements in a rectangular weir near the mouth of Wignell Drain from May to October and stable isotopes of water sources were collected biweekly. Isotope ratios were used in a two-component mixing model to calculate the fraction of groundwater and near-surface water as well as perform hydrograph separation using discharge measurements. The Wignell Drain water was mostly near-surface contributions (78%) except in the spring where groundwater made up 77% of the drain water. While total phosphorus consistently exceeded provincial guidelines (averaging 0.3 mg/L), the timing of elevated E. Coli observed in the Wignell Drain coincided with large rain events and predominant near-surface water contributions.