Analysis of fossil diatom assemblages recovered from a 12.2 m core reveals a series of distinct floristic associations. The associations present are correlated with sediment type and reflect successive stages in the development of the lake. A basal red clay sediment contains a planktonic association characteristic of large, proglacial lakes. At 10.0 m core depth, sediment type changes to fine sand containing a higher abundance of benthic species indicating reduction of water depth at the deposition site. Marl sediments begin at 9.7 m and contain an association characteristic of a small, shallow, oligotrophic lake. At 8.8 m the marl sequence is interrupted by highly organic sediment containing a eutrophic plankton association. From 8.5 to 7.6 m the sediment type grades from marl to organic, apparently reduced sediments and diatom associations present contain successively higher percentages of planktonic species associated with eutrophic habitats. By the 7.6 m level a eutrophic plankton association, similar to the modern flora, is established and remains remarkably constant to the surface of the section.