Restoration and the creation of artificial wetlands can mitigate the loss and degradation of natural wetlands. The chief wetland areas in northern Iberia are the estuaries situated along the coast of the Bay of Biscay. These areas are tidal in nature and often small in size. These characteristics, together with high levels of human, disturbance can cause significant limits on the conservation of waterbirds. At the end of 2009, an old polder within the Urdaibai marshes in Spain was modified to create an artificial lagoon (Orueta Lagoon). The goal of this study was to evaluate the use of this lagoon by waterbirds, and its contribution to waterbird assemblage and richness at Urdaibai. Orueta Lagoon contributed 26.8% of total abundance, including 11 species not present in other zones of Urdaibai. Thus, it provided a new and attractive habitat for several waterbird species, especially ducks, coots and allies, shorebirds and grebes. Therefore, Orueta Lagoon plays a fundamental role in the enrichment of the waterbird assemblage at Urdaibai and hence is of great value from a conservation standpoint.