We set out to explore whether the inclusion of perceptions into risk assessment might be a key to unlocking the human factor in the vectoring of aquatic non-indigenous species. To this end, we developed a risk assessment model that used people’s perception of concern and stated behavioural intentions to measure consequence. We trialled this risk model using a test scenario of the non-indigenous species Didymosphenia geminata (a freshwater diatom) being introduced to Tasmania, Australia: a location where it is currently not present. Likelihood was determined by calculating the probability of Didymosphenia entering the test region based on exposure to D. geminata (travel history of arriving air passengers and the passenger’s participation in freshwater recreational activities) and mitigation activities (whether their recreational equipment had been washed). The likelihood of a Didymosphenia incursion into Tasmania was determined to be rare. Consequence was determined by targeting three recreational user groups that participate in activities related to the movement of this species in other countries: trout anglers, hikers, and kayakers. Consequence was measured as respondent’s level of concern and stated behavioural intentions if the respondent was confronted with an incursion of Didymosphenia. The consequence of a Didymosphenia incursion ranged from moderate to catastrophic. Thus, the total derived risk was determined to be low-medium. The use of perception to inform the consequence component of the risk assessment proved useful as individuals behaviours are often attributable to the introduction of species, and thus are an important consideration for risk management and education. At a local level these outcomes provide direction to biosecurity of unregulated pathways. At a global level, this risk assessment is a useful tool to assess the potential vectoring of a nonindigenous aquatic species, and potential human actions that might impede the management of a non-indigenous species once it crosses a border.