Seasonal fluctuations of the epipelon in five eutrophic, prairiendash;parkland lakes were characterized by spring and late summer ndash; autumn maxima, although midsummer peaks, dominated by chlorococcalean algae, occurred at the shallow stations in three lakes. Winter peaks were invariably dominated by algae of planktonic origin. The epipelon was light limited at the deep stations under ice cover during the winter. More correspondence than in previous studies was found between the standing crop and the nutrient status of the overlying water but no one single factor could account for seasonal fluctuations of the epipelon. Instead, a combination of light levels, nutrients, temperature, physical disturbance, and biotic interactions affected these fluctuations. The mean standing crop size of the epipelon was closely related to the mean bicarbonate levels.
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