Phytoplankton monitoring has extended to practically all the regions of the European coast due to the implementation of the European Water Framework Directive. In this way, the study of phytoplankton taxonomic composition and dynamic is being performed in many areas poorly studied or not studied before. During the last years, a monitoring programme has been carried out at the coast of Cantabria region (SE Bay of Biscay); the presence of some potentially toxic and bloom forming species (>7.5×10(5)cells per litre) has been observed. Diatoms and cryptophytes are the main blooming taxa in this region in the majority of the estuaries and in some of the coastal sites. All estuaries and coastal stations showed at least one potentially toxic species, being the dinoflagellates the group with the highest number of taxa observed. The potentially toxic species found in highest concentrations were the genera Pseudo-nitzschia and Chrysochromulina.