Freshwater invaders threaten both natural ecosystems and human activities. An invasive freshwater sponge Heterorotula multidentata (Weltner, 1895) has been found for the first time in continental waters of Europe (Spain). It is a species native to Australia and New Zealand, from which it spread to Japan, being considered invasive. The species has been found in water intake grids of irrigation and drinking water systems in the basins of the Guadalquivir and Tajo rivers, affecting their hydrological functions. It has also been found growing on the invasive mussel Dreissena polymorpha in the Guadalquivir River. To assess the risks associated with invasive alien organisms, a detailed knowledge of their taxonomic status and distribution is necessary. A morphological and molecular evaluation confirmed that the specimens found in Spain belong to the Japanese type. A full morphological description and the fouling problems caused by the species are also provided. It is not yet clear how H. multidentata arrived at Spain, but indirect transport by other invasive freshwater species cannot be ruled out either, as H. multidentata has been found fouling the invasive species zebra mussel.