Recent investigations of Lake Erie in the winter have demonstrated the occurrence of substantial phytoplank-ton communities largely consisting of the diatom Aulacoseira islandica (O. Müller) Simonsen. To assess the ac-tivity of this diatom community, multiple measures of production, both general and diatom-specific, were undertaken. We measured oxygen (O 2) evolution as proxy for carbon (C)-fixation and 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl) methoxy)-phenyl)oxazole (PDMPO) incorporation as a measure of silica (Si) deposition. The latter demonstrated conclusively that diatoms were active during winter months and confirmed that diatoms are the primary drivers of winter productivity. The stoichiometric relationship between carbon and silica in the winter Lake Erie phytoplankton assemblage was further compared to the ac-tivity of the summer community. Although the winter phytoplankton community was observed to be active, it was less active than the summer community, with lower measured rates of O 2 evolution and Si deposition. These findings provide a new and expanded understanding of the biological carbon production in Lake Erie.