Slowed aquatic invasion coincides with intensified research and prevention in Minnesota, USA

Prevention is often the most cost-effective expenditure of limited environmental management resources. While demonstrating that harms occur without prevention is relatively straightforward, showing harms have lessened due to prevention--proving its effectiveness--is not, in part because it requires counterfactual data (i.e., quantification of harms that did not occur and then attributing these to prevention). Here, we attempt to measure aquatic invasive species (AIS) prevention effectiveness in Minnesota, USA, where AIS, their management, and research have increased since the 1980s. We showed the rate of new aquatic invasions slowed alongside intensified prevention investment starting around 2015. Further, mechanistic simulations grounded in real boater movement and boat inspection effectiveness data suggested prevention may have reduced new invasions of two high-priority AIS by 20-53% over a ten-year span. We argue our evidence strongly supports long-term statewide prevention, monitoring, and research.