Eutrophication is currently thought to be one of the leading causes of water quality impairment in North America. Fertilizer and manure high in nutrients such as phosphorus is recognized as one of the primary drivers of this issue. This thesis aimed to assess the influence of agricultural land use on phosphorus loss to streams and groundwater at 5 different sites throughout the course of one year in Ontario, Canada. Streams flowing through agricultural landscapes were found to have elevated phosphorus levels, with concentrations exceeding important ecological thresholds for eutrophication for almost the entirety of the sampling period. There were observed seasonal patterns in phosphorus levels at all sites, with high concentrations during the non-growing season, predominantly in the dissolved form. Vegetated buffer strips were found to have variable efficacy during this portion of the year, highlighting the need to better understand the performance of mitigation strategies in temperate regions.