In a previous paper, we presented a very simple monitoring system. That system aimed at providing the basic information needed to set up a hydrological simulation model that would be used to understand the behavior of the system and to explore possible changes linked to future climates. After more than 1.5 years of observations, the gathered information was utilizable to test a 0D hydrological model. This exercise is presented here, together with a comparison with a more refined, and more demanding, 2D hydrodynamic model, enlightening strengths and weaknesses. Several details are revealed in this paper showing how even a simple case needs some type of art in order to overcome the unavoidable difficulties. Surprisingly nice answers have been obtained that illuminate the behavior of the lagoon and shed light on the key points to be improved both in monitoring and modelling. This exercise can be of help in several similar situations.