1. A canal control system for controlling the water level or water flow in a canal system, comprising: (a) a centralized master controller, (b) a local slave controller, (c) a wireless communication system between the centralized master controller and the local slave controller, (d) a (fixed) reference point or a (movable) marker relating to the water level or water flow in the canal system, and (e) an adjustable actuator in the canal system, such as an adjustable gate or pump, whereby the local slave controller comprises a mobile, wireless device that in turn comprises (i) technical means for viewing or recording a measurement of the water level or water flow relative to the (fixed) reference point or (movable) marker in the canal system, (ii) technical means for sending the measurement of the water level or water flow as an input signal to the centralized master controller, (iii) technical means for receiving an output control signal from the centralized master controller, and (iv) a user interface for displaying a human-readable instruction based on the output signal received from the centralized master controller.