This paper presents empirical material of the role of canal operators, canaleros, in one irrigation scheme in Mexico over a period of two decades. The open canal infrastructures are fitted with manually operated adjustable gates and intakes. During the period of observation, both management set-up and the canal infrastructure changed. The case of the canalero shows how low-ranked field personnel play an important role in scheduling and implementing water distribution. The canalero emerges as a key actor who makes the system work. Canaleros have created their own semi-autonomous field of action; an area of competence from which they derive a certain degree of authority. The case study findings are compared with relevant published sources complemented with electronic interviews with experts. In large- and medium-scale open canal irrigation systems with flexible and manually operated irrigation devices, positions similar to those of the canalero exist. Canal operators seem to play similar key roles yet no systematic review or comparative analysis of their position exists. This paper makes a first contribution to explain why such field level staff can perform such significant roles and continue to do so.