Two ministers from France's government have flown over oil slicks that they're worried could land on Corsica's coastline.
Two navy ships that set off from the port of Toulon are sailing towards them with special equipment to attempt to clean them up.
The spills, which are 35 kilometres long, were made deliberately by ships trying to save money by dumping used oil overboard rather than having it removed in port.
"These are used oils that are found in the holds and which normally have to be degassed in the ports. There are installations for this purpose to empty the holds.
"However, some people, in order to make some savings, empty this into the sea and this is what is happening today," said Barbara Pompili, France's Minister of Ecological Transition.
The slicks were discovered on Friday and by Saturday night the currents were keeping them offshore, but officials warned that the direction of the sea currents was liable to change.
France's Minister of the Sea said they were determined to catch the perpetrators.
"We have arrived here determined to find those who have been wildly discharging oil. As I said earlier, they are thugs and they will have to be treated like thugs," Annick Girardin said.
"As I speak, we have three ships that will have to be checked as soon as they arrive in their port of destination and we will know more."
Beaches popular with tourists along Corsica's eastern coastline are now closed and fishing has been banned.
Around 80 members of the security and rescue services have been drafted in to help clean up should the oil reach the coast.