Fatigue may influence risk perception for subsequent physical activities. Participants volunteered to fill out a questionnaire, rating the perception of risk of cycleway pictures either before or after running a half or a full marathon race. The after race running group also reported workload, flow state, and stress state measures. We found the runners who responded after the race rated the cycleways as riskier than those who responded before the race. This effect was partially moderated by the length of the race run; runners who ran a full marathon were more likely to rate the cycleways as personally risky. The full marathon runners also reported more physical and mental fatigue than the half-marathon runners, but interestingly, they rated the race as less mentally and physically demanding. Fatigue may impact the perception of physical risks.