In solving a variety of problems people interact with their external environment, often using artefacts to supplement and augment their problem solving skills. The role of interactivity in problem solving was investigated using a river-crossing problem. All participants performed the task twice, once in a high interactivity condition and once in a low interactivity condition. Moves to completion were higher in the high interactivity condition but latency per move was much shorter with high than with low interactivity. Moves in the world were easier to implement than to simulate mentally and acted as epistemic actions to facilitate thinking. In addition, when participants experienced the low interactivity version of the task second, their performance reflected little learning. However, when the high interactivity version was completed second, latency to solution and latency per move were substantially reduced. These results underscore the importance of investigating problem solving behaviour from a distributed cognition perspective.