Reservoirs are human-made freshwater ecosystems that are important sentinels of climate change. Reservoirs biogeochemically behave along a continuum of lotic to lentic ecosystems. Because of this hydrologic variability, recent research efforts have highlighted key catchment, waterbody, and management attributes that separate reservoir biogeochemical responses to climate change from lake ecosystems. These reservoir-specific attributes can include larger catchment area to surface area ratios, shorter hydraulic residence times, and large fluctuations in water level resulting from management practices. In addition to these reservoir-lake differences, reservoir hydrologic regime can differ based on whether a pre-existing river or lake was dammed, and this hydrologic distinction tends to determine whether a reservoir will reflect biogeochemical patterns more similar to rivers vs lakes. Little is known about how changes in hydrologic regime will impact reservoir biogeochemistry. Thus, we investigated how variation in hydrologic regimes influences spatiotemporal variability of water quality parameters at multiple scales in two hydrologically distinct reservoirs. To address this topic, we leveraged three types of limnological data - spatially-explicit, temporal high-frequency, and vertically-integrated - sampled over two growing seasons (2023 & 2024). We observed the largest spatial and temporal variation in temperature, dissolved oxygen, turbidity, and chlorophyll-a in a run-of-river reservoir than a reservoir formed from a dammed natural lake. However, patterns differed across water quality variables. Temporal variation obscured spatial trends in water temperature, while spatial variation was greater than temporal for chlorophyll-a and turbidity in both water bodies. These findings suggest that physical and biological processes occurring both internally and externally interact to dictate ecosystem structure. This work contributes to our understanding of the hydrologic influence on reservoir biogeochemistry and provides context for how reservoirs may differentially respond to climate change.