Crawford Lake, situated within the Crawford Lake Conservation Area near Milton, Ontario, Canada, has unique characteristics that make it ideally suited to high-resolution paleoecological studies. The seasonally deposited varved sediments in the deep basin of this meromictic lake are currently being considered as a potential Global Boundary Stratotype Section and Point (GSSP) to mark the lower boundary of the proposed Anthropocene Epoch. Golden-Brown Algae (Chrysophyte) communities were examined at annual resolution in varves spanning 1930-1990 CE from freeze core CRW19-2FT-B2, collected from Crawford Lake in February 2019. Stratigraphically constrained cluster analysis showed major assemblage changes within this interval, with one of the highest magnitude changes occurring between varves deposited in 1952 and 1953, coinciding with the global effect of atmospheric nuclear armament testing on deposited isotope signatures, one of the key markers of the proposed Holocene- Anthropocene boundary. The post-1953 species assemblages within this lake were novel...