Excess loading of nutrients into lakes is one of the biggest threats to the quality of freshwater and the associated ecosystems. In general, phosphorus (P) is considered the limiting nutrient for primary productivity in freshwater systems and has been recognized as one of the main contributors to excessive algal growth in temperate lakes. Contributions by groundwater seepage are rarely addressed in conventional approaches to address nutrient loading to lakes, due largely to the logistical challenges of determining groundwater exchanges at the sediment-water interface. However, where studied, groundwater has been shown to be a key element of a lake’s nutrient dynamics, with a direct and significant impact on littoral communities.In this dissertation I investigated the role of groundwater seepage in the P loading dynamics along the shoreline of Oneida Lake, in central New York, during the summer seasons of 2017, 2018 and 2020. I first explored the potential of groundwater seepage to carry P into a 700m stretch of the shoreline associated with three different adjacent land uses, by directly measuring groundwater seepage flow using seepage meters, and collected groundwater samples to analyze for its P content using pore water samplers. Samples were analyzed for both Total Phosphorus (TP) and Soluble Reactive Phosphorus (SRP). Synthesizing these data, I estimated groundwater P loads into this segment of the Oneida Lake shoreline, and then analyzed the relationship between the observed loads and possible controlling factors, including precipitation, shore adjacent land uses, and distance from the shore. As the next step, I expanded the analysis throughout the entire Oneida lake shoreline, by using the same methods to estimate loads at ten representative locations around Oneida Lake’s 88 km long shoreline. Results indicated that groundwater seepage is a continuous source of dissolved P throughout the sediment-water interface of the entire Oneida Lake shoreline. SRP represented a very small fraction, but TP concentrations and loads were extremely high, suggesting that dissolved organic compounds were the primary source for groundwater P. Groundwater seepage flows and its loading were highly variable both across space and time, which was partially explained by adjacent land uses and precipitation patterns. This constant input in the littoral region of the lake has elevated the concentrations of P in the associated nearshore surface waters and may be influencing phytoplankton development including cyanobacteria, and another biota. Estimated loads were then integrated into a comparison of the groundwater phosphorus inputs, with surface water inputs associated with the five main tributaries to Oneida Lake to better understand the relative contributions from these two different sources. Results suggested that groundwater contribution of dissolved phosphorus, and specifically TP, to the lake shoreline is comparable to tributary contributions, particularly during baseflow conditions. My research concludes that groundwater seepage is a significant source of dissolved P to Oneida Lake and may be a crucial factor aiding to maintain summer primary productivity, and algal blooms in temperate lakes.