The bottom sediment from three coring stations in Lake Lugano (Lago di Lugano) show major differences in their role in the P-cycles related to their geochemistry and characteristics of sedimentation. In the northern basin, the deepest sediment may be considered practically “inactive”, due to a permanently reduced condition at the sediment-water interface. In the southern basin, the sediments are “active” with respect to P-recycling with strong seasonal variations. One of the sites (Figino) behaves as a sink for P due to a high iron content and an important rate of detrital sedimentation.