Illegal bushmeat hunting is a global threat to wildlife, but its secretive and unregulated nature undermines efforts to mitigate its impacts on wildlife and wildlife-based industries. We investigated the scale of illegal bushmeat hunting in the Okavango Delta, Botswana (~ 20,000 km2) to assess its potential contribution to wildlife population declines. Approximately 1,800 illegal hunters each harvest an average of 320 kg of bushmeat annually, though some reported harvesting ≥ 1000 kg. While impala were the most commonly hunted species, buffalo and greater kudu accounted for most bushmeat. Hunters remove ~ 620,000 kg of medium-large herbivore biomass (equivalent to 15,500 impala) annually from the delta and humans are the fourth most prominent predator in the delta. Cumulative harvest by humans and other predators likely exceeds the intrinsic population growth rate of several species of ungulates in the delta, and helps explain purported declines in ungulate populations. Competition between humans and other apex predators for limited prey reduces the ecosystem's carrying capacity for large carnivores. Illegal bushmeat hunting represents an economically inefficient use of the delta's wildlife and a threat to the region's tourism industry. Strategies are required that provide clearer avenues for communities to benefit legally from wildlife, while concurrently curbing illegal hunting through effective law enforcement.