Parasite prevalence in an intermediate snail host is subject to multiple anthropogenic stressors in a New Zealand river system

•Highest parasite prevalence at high farming intensity and low water abstraction.•Observed antagonistic response pattern highlights importance of stressor interactions.•Average prevalence of all parasites infecting Potamopyrgus in the catchment was 5%.•Host–parasite systems are a promising tool for detecting multiple-stressor effects.