As the acute phase of the emergency subsides, Milan's Naviglio Grande faces a hefty cleanup bill. The alarm was raised on Friday when a 28-kilometer-long black oil slick crept down the canal from Magenta all the way to Milan’s Darsena basin. Prosecutors have opened an environmental pollution probe to uncover the source of the spill, while regional authorities await tests from the ARPA environmental agency to confirm the exact substance, most likely diesel fuel.

Initial theories suggested an accidental pipeline rupture during site remediation works, but the absence of pressure drops and the fact that the spill stopped on its own have pushed investigators toward a darker hypothesis: deliberate dumping. The sheer volume suggests illegal disposal directly into the sewer network, likely from a tanker truck emptied in an unauthorized spot or an uncleaned storage tank.

Firefighters and Civil Protection crews successfully contained the slick using floating barriers and absorbent booms. Skimming contaminated water from the canal, technicians filled four tanker trucks with roughly 120 tons of hazardous material. Disposal and treatment operations, managed by the Villoresi Consortium, are expected to exceed €100,000, a bill footed by the Lombardy Region. While the neighboring Naviglio Pavese remained unscathed, test results will help assess environmental damage and track down those responsible. Meanwhile, Milan Civil Protection Commissioner Marco Granelli called for stronger institutional coordination.