Factors which affect the distribution of benthic algal communities in acidic lakes have been largely unexamined. This study was designed to examine the environment of the epipelon in such lakes and to determine the factors that structure this community. In four acidic lakes in northern Michigan, water samples were collected at the sediment surface and 10 cm above the sediments by diffusion through a membrane into bottles for 20 days. Sediment cores were taken and the pH was measured at the sediment surface and the overlying water. In most lakes, higher concentrations of phosphorus, nitrate, ammonia, and silica were found at the sediment surface, and the pH varied (+-0.5 pH units) from the water column. In a growth chamber experiment, benthic algae was subjected to combinations of light levels (approximately 50-100 uein/m2/s) and dissolved organic carbon concentrations (approximately 6-12 mg/L DOC) for 21 days. Diatom biovolume increased significantly in shaded treatments (regardless of DOC), while blue-green algae increased significantly in biovolume in the high-light treatments (regardless of DOC). In four acidic lakes in northern Michigan, we investigated the effects of light and nutrients on benthic algal communities. A series of light filters was placed just above the sediment of each lake at a depth of 2-3 m in order to filter out 0.0%, 80%, and 90% of light reaching the benthos. In an additional experiment involving the same lakes, nutrient-diffusing devices were deployed, which allowed epipelic communities to experience increases in P, N, P+N, labile carbon, and refractory carbon. For each experiment, algal samples were collected from all treatments after several weeks and subsequently counted and identified. It was determined that light could account for most of the variance in algal biomass (r2=0.79). High-light conditions promoted filamentous green algal growth, while diatoms had a relatively greater abundance in lower light conditions. Nutrients (mainly phosphorus and labile carbon) can limit benthic algal biovolume in lakes with high light penetration, but become less of a factor in lakes with low light penetration.