Animal subsidies have important effects on aquatic food webs, yet we know little about how these effects vary with the magnitude of subsidies. The Mara River in Kenya has over 4000 hippopotamuses who forage on savanna grasslands during the night and rest in the river during the day. We selected six sites along the hippo abundance gradient (from 0 to 4300 hippos) in the Mara River and measured invertebrate biomass, production, and diversity at each site. Hippo dung increased from 0 to 70 g of dry mass/m2, which resulted in a > 10-fold growth in invertebrate biomass. Invertebrate production increased exponentially from 840 mg/m2/year to 7080 mg/m2/year at the site with the highest hippo dung. These changes in production were strongly driven by increases in scrapers like the Tricorythid mayflies, while other functional feeding groups increased to a lesser extent. The number of invertebrate species doubled at sites with hippo dung, but they did not change with the magnitude of the subsidy. Lastly, the density of invertebrates within hippo dung itself did not vary across the gradient, although invertebrate density in hippo dung did increase during high discharge periods. These patterns indicate that it is not just the occurrence, but the magnitude of animal subsidies that play an important role in structuring freshwater macroinvertebrate communities.