In this paper a mathematical model of the water level variation in the first pool of the Aragon's Imperial irrigation main canal belonging to the Ebro Hydrographical Confederation (Spain) is derived from system identification experiments. The complete identification procedure from experiment design to model validation taking into account prior physical information is presented. It is shown that a linear second order model with an ARMAX structure and a time delay describes adequately the main dynamical behavior of this canal pool. The obtained model will be used for prediction and control purposes. Copyright © 2007 IFAC.