Managing natural systems is fundamentally an exercise in managing the human behaviors that affect those systems. In particular, the human-mediated movement of live animals, vectors, or infectious material is a well-documented vector for the spread of invasive species and emergence of novel pathogens in many contexts, but especially in inland freshwater systems. Accordingly, the increasing rate of biotic invasions in these systems is an ongoing challenge that requires an understanding of the human behaviors that facilitate their spread. We assessed whether the illegal release of live baitfish, a common behavior among recreational anglers that risks the spread of invasive species and pathogens, could be explained by the Theory of Planned Behavior (TPB). We implemented a survey of licensed recreational anglers in Minnesota, USA (n=8000) and analyzed the results with structural equation modeling to assess the relationships between attitudes, subjective norms, and perceived behavioral control and intent to release live baitfish. We received 1,691 (adjusted response rate=22%) responses and found that 32% of anglers had released baitfish at least once in the past year, and 16% expected to release live baitfish in the future. Overall, the TPB model explained 66% of the observed variation in baitfish release intent. Subjective norms were the most important predictor of release intent in the whole group model, and were particularly important among anglers who did not know about the legal prohibition of live baitfish release. Knowledge of baitfish disposal regulations was also associated with significantly lower intent to release scores. We also found that misperceptions of the benefits of live baitfish release, e.g. providing food for wild game fish, were relatively common and associated with positive attitudes towards live baitfish release. Our findings suggest that education and awareness campaigns that use normative messaging and/or correct these misperceptions could be highly effective in curbing illegal baitfish release behavior among anglers in this population.