For tourism in parks there are many lists of potential ecological indicators that have not been implemented in practice, many systems of management indicators with little ecological basis or significance, and many ecological studies of recreational impacts that do not provide management indicators. Indicators that are both scientifically defensible and feasible and valuable in management, however, are very rare. Broad-scale indicator systems developed for tourism ecolabels and environmental accreditation schemes are inadequate for testing the impacts of people in parks. Monitoring visitor impacts needs ecological baseline data that incorporate seasonal cycles, long-term trends, extreme events, and internal patterns. It needs indicators that reflect the priority conservation values of the protected areas concerned, and the types of use, not merely management processes. It needs specific indicators that are discriminating, quantifiable, actionable, sensitive, ecologically significant, integrated, and feasible in practice. And it needs experimental design that distinguishes tourist impacts from other sources of variation. Interested and experienced rangers and volunteers can make a major contribution to such monitoring programmes, but reliable ecological monitoring needs qualified ecologists.