The communities of diatoms preserved in sediments serve as indicators of historical water chemistry, temperature, and hydrology. As part of a larger cross-regional study of post-industrialization climate change, we cored the sediments of a floodplain oxbow lake in Alabama. Our working hypothesis for this lake was that it would show minimal effects from climate and hydrological changes over its life span. However, our analyses of diatom composition and radiocarbon dating suggest that the lake has gone through a series of hydrological and temperature changes. Prior to ~3000 BCE, sedimentation was low and diatom communities were characteristic of lotic conditions. After ~3000 BCE, sedimentation increased and the diatom community became dominated by more pelagic species and species tolerant of turbid waters. These data suggest that the oxbow was actively connected to the river channel prior to ~3000 BCE but then became isolated. Additionally, between 900-1300 AD, the diatom community shifted from aerophilic, cold water species to warm water species, coinciding with the Medieval Climate Optimum. In contrast, the opposite occurred between 1650-1850 AD, coinciding with the Medieval Climate Minimum. Further examination of other sediment core features (e.g., stable isotopes) will reveal whether these conclusions based on diatom data are justified.