**3.6 Conclusion**

This case study applied ecological multi-metric indices recommended by the European Commission (2008/915/EC) to two reservoirs of the Guadiana watershed, which have repeatedly developed cyanobacteria blooms in the summer, in association with high hydraulic retention. Values for the ecological potential measured by these indices ranged from Bad (> 9% contribution of cyanobacteria biovolumes) to Good (InGA) and Very Good (InGA and MedPTI). However, these indices do not provide insight on appropriate CHAB prevention and mitigation measures. Instead, long term monitoring of ecological data, was necessary to propose appropriate countermeasures. In fact, in these two reservoirs the only effective measure to prevent or mitigate CHABs was to reduce water residence time by discharging surface water.
