The composition, spatial distribution and source of marine litter in the Spanish Southeast Mediterranean were assessed. The data proceed from a marine litter retention programme implemented by commercial trawlers and were analysed by GIS. By weight, 75.9% was plastic, metal and glass. Glass and plastics were mainly found close to the coast. A high concentration of metal was observed in some isolated zones of both open and coastal waters. Fishing activity was the source of 29.16% of the macro-marine litter, almost 68.1% of the plastics, and 25.1% of the metal. The source of the other 60.84% could not be directly identified, revealing the high degree of uncertainty regarding its specific origin. Indirectly however, a qualitative analysis of marine traffic shows that the likely sources were merchant ships mainly in open waters and recreational and fishing vessels in coastal waters.We are grateful for the support of the PESCAL Project by European funds through General Secretary of Fisheries of Spain, led by CETMAR with the participation of the Joint Research Unit between the Spanish Oceanography Institute (IEO) and the University of Alicante (UA). Santiago García-Rivera was supported by PESCAL Project and a PhD grant from the University of Alicante
