© 2021 John Wiley & Sons Ltd.Intraguild predation (IGP), defined as killing and eating among potential competitors, is commonly observed in shallow lakes and is predicted to dampen trophic cascades and affect ecosystem properties (e.g. phytoplankton biomass or primary production). We tested this hypothesis by manipulating the density of two common lake predators, the small-sized fish Pelteobagrus fulvidraco (the intraguild predator) and the shrimp Exopalaemon modestus (the intraguild prey), in outdoor mesocosms containing natural phytoplankton and zooplankton communities. In single predator treatments, both predators induced a strong trophic cascade, as evidenced by extinction of the key herbivore, Daphnia pulex, and increasing phytoplankton biomass and chlorophyll a concentration. When the two predators were added together, however, the strength of collective predator effects on zooplankton and the cascading effects on phytoplankton growth were weaker than the sum of the individual predator effects. We attributed this antagonism among predators to intraguild predation as demonstrated by the lower shrimp catch per unit effort in the presence of fish. Our study suggests that common predators in subtropical shallow lakes may act antagonistically and thereby dampen trophic cascades in food webs. Thus, when implementing biomanipulation efforts to suppress algal growth via enhancing zooplankton herbivory, both the quantity and diversity of lake predator assemblies should be considered.