The importance of extending physically based approaches to catchment management to include social considerations has recently been highlighted alongside increasing legislative pressure to utilise public participation in river management processes. Nine water managers, operating at varying geographical scales, from the UK and north-west Europe were interviewed to determine their approach to, opinion of, and success in utilising public participation for decision making. The results indicate that despite variations in approaches to, and perceptions of, participation, one dominant factor constrained the use of higher level participation: scale. The results demonstrate that the degree of participation and influence for ‘non-certified’ experts was inversely proportional to the scale of the project. This was attributed to issues of practicality in communicating between a large number of individuals, but also to underlying factors such as availability of financial support and governing regulations that differ between organisations of different sizes. The findings were used to consider the role of Callon's public education, public debate and co-production of knowledge models of scientific knowledge production (Callon 1990). It is suggested that, for practical application, traditional models be developed into more reflexive approaches that account for the complexity of real-world situations.