France participated to the first and second intercalibration rounds of the Mediterranean Geographical Intercalibration Group (GIG) for phytoplankton in natural lakes. During the process it was rapidly defined that no intercalibration exercise was possible for lakes. Only two intercalibratable methods were available (for Italy and France) with very few sites and no reference sites. In this context, this report describes the IPLAC methodology and the impossibility to realize the intercalibration process in the case of natural Mediterranean lakes.