Ultraviolget (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 UV radiation early in colonization, but after 45 days of accumulation, the biomass of UV-exposed and UV-shielded algal communities did not differ signficantly. Algal taxa differed in their sensitivity to UV radiation. Cell densities of Synedra ulna, S. radians, Cyclotella comensis, and the Epithemiaceae were signficantly reduced by ambient UV radiation. Achnanthidium minutissimum appeared to be stimulated by exposure to UV radiation. Differential responses of diatom taxa may have important implications for littoral zone food webs.