Anthropogenic changes in the nitrogen (N), phosphorus (P), and carbon (C) cycles have altered nutrient concentrations and the light climate in freshwaters globally. These factors influence phytoplankton (PPr) and bacterial production (BP), which constitute the basal energy resource for higher trophic levels in the pelagic zone of lakes. The light:nutrient hypothesis (LNH) predicts that although basal production will decrease at low light, seston C:nutrient ratios also decrease, thus increasing food quality for crustacean zooplankton, which tend to have relatively fixed C:nutrient ratios. We tested the LNH in a mesocosm experiment by examining the effects of N, P and C additions and shading on PPr, BP, seston C:nutrient ratios and zooplankton biomass in an oligotrophic clear water lake. We found that zooplankton biomass was strongly reduced in shaded treatments. Although PPr was unaffected by shading, BP decreased with shading. Bacteria can be an important energy and P source for zooplankton when mobilized through intermediate trophic levels, and correlations between BP, bacterial biomass, ciliates and zooplankton support this. Seston C:nutrient ratios were not affected by shading, possibly due to a high abundance of mixotrophic phytoplankton across treatments. Shading shifted the phytoplankton community towards low light adapted, but potentially less edible phytoplankton species, such as colony forming Dinobryon (Chrysophyta) and gymnoid (Dinoflagellata) taxa, which were negatively correlated with zooplankton biomass. Thus, the LNH may be inadequate when predicting changes in crustacean zooplankton biomass in response to light and nutrients in oligotrophic systems, where Daphnia is rare and mixotrophic phytoplankton are abundant.