In this paper, a gain-scheduled Smith Predictor PID controller is proposed for the control of an open-flow canal system that allows for dealing with large variation in operating conditions. A linear parameter varying (LPV) control-oriented model for open-flow canal systems based on a second-order delay Hayami model is proposed. Exploiting the second-order structure of this model, an LPV PID controller is designed using and linear matrix inequalities pole placement. The controller structure includes a Smith Predictor, real time estimated parameters from measurements (including the known part of the delay) that schedule the controller and predictor and unstructured dynamic uncertainty, which covers the unknown portion of the delay. Finally, the proposed controller is validated in a case study based on a single real reach canal: the Lunax Gallery at Gascogne (France).