- Understanding the relationships between land use, water quality, and groundwater is crucial for ecological, economic, and water management decisions. This study aims to provide a comprehensive analysis of the land use activities and hydrologic processes influencing the water quality of Oak Creek watershed. Objectives of this study were: 1) to determine land use influence on stream water anion concentration along a longitudinal gradient; 2) to assess potential effects of stream-aquifer interaction on stream water quality; and 3) to determine potential origins and seasonal variability of surface water flow. Water samples were collected between January 2018 and November 2019 from 22 stream sites and 19 shallow groundwater wells in Oak Creek watershed spanning forested, agricultural, and urban land use. All samples were analyzed for anion (i.e., chloride, sulfate, nitrate, phosphate) concentrations and stable isotopes of water. Results indicate that: 1) Oak Creek acts as an integrator of precipitation received in high elevations and incoming ground and surface water sources as it moves downstream driving overall stability of isotopic compositions but leading to increasing chloride and sulfate concentrations; 2) shallow groundwater in agricultural settings exhibits high spatial variability; and 3) land use – water quality relationship are complex and temporally variable.