The invention relates to a canal control system for controlling the water level or water flow in a canal system (2), comprising: (a) a centralized master controller (20), (b) a local slave controller (30), (c) a wireless communication system between the centralized master controller and the local slave controller, (d) a (fixed) reference point (8) or (movable) marker (11) relating to the water level in the canal system, and (e) an adjustable actuator (9) in the canal system, such as agate or pump, whereby the local slave controller comprises a mobile device (13) capable of displaying a human-readable instruction which an operator can act upon to set the adjustable actuator. The operator takes a picture of the water level and/or of the setting of the adjustable actuator. The data of the picture is used for updating a mathematical model of predictive control of the canal system and for calculating the setting of the present actuator and for determining which actuator is to be visited next by the operator.