Ultraviolet (UV) radiation levels were manipulated in the littoral zone of a low-elevation, mid-latitude glacial lake. Benthic algal biomass accrual was significantly inhibited by ambient levels of W radiation early in colonization, but after 45 days of accumulation, the biomass of W-exposed and W-shielded algal communities did not differ significantly. Algal taxa differed in their sensitivity to UV radiation. Cell densities ofSynedra ulna, S. radians, Cyclotella comensis, and the Epitherniaceae were significantly reduced by ambient UV radiation.Achnanthidium minutissimumappeared to be stimulated by exposure to UV radiation. Differential responses of diatom taxa may have important implications for littoral zone food webs.