The plot of the LWQI corresponding to the above mentioned one-year simulation is shown in Fig. 4. By comparing it with Fig. 3, one may note that the index is worse when the system shows bad health status, like during anoxic crises. It is worthwhile to stress that, to perform multicriteria analysis, the LWQI is averaged over the length of the simulation. Since the deterioration of water quality in recent years has determined the death of phanerogams in the lagoon, phanerogams coverage is neglected in LWQI computations.