A study by the UPV/EHU's Department of Plant Biology and Ecology has evaluated the response of Urdaibai estuary phytoplankton to the changes brought about after the closing-down of the Gernika wastewater treatment plant; a novel tool based on pigment analysis and developed by the Phytoplankton Ecology group was used. The results show that the physicochemical quality of the water has improved and this has led to changes in the phytoplankton community that are heading in the right direction.