In the summer of the 2002 Ebro river presented historical minimum volumes. The Hydrographic Confederation of the Ebro (C.H.E.) ordered to URS the accomplishment of a campaign of sampling to determine the ecological state of the fluvial section between Zaragoza and the backwater caused by the swamp of Mequinenza. This section is specially sensible to the diminution of the volume since it is receiving numerous urban and industrial spills of the area of Zaragoza, in addition is of an area of natural interest (Sotos and Galachos of the Ebro). The sampling was made days 31 of July and 1-2 of August of the 2002, with volumes between 14 and 20 m3/s.