Watersheds have always been an object of study for their strongly unequal dis-tribution of environmental "bads" between upstream and downstream areas. The Po valley is an exemplary case: with a succession of sources of pollution and artifi-cial and natural purification systems, many polluters and many territories serve as downstream collectors. The article discusses the conflict over water pollution be-tween the Po Delta area of Polesine (Veneto Region) and the city of Milan, which has developed through a series of trials. The conflict was solved before the end of the civil cases, when the city of Milan introduced important purification systems. However, this dispute was followed by other environmental and judicial issues. Production and disposal of sewage sludge from the urban waste water treatment provoked a respatialisation of environmental injustice. Pollution - this time in the form of sludge - results again disposed of in fragile areas that, differently to Polesine, are located in the Lombardy Region, to which Milan also belongs.
Keywords: Polluters, downstream collectors, fragile areas, respatialization of en-vironmental injustice, Po Delta