It makes the mussels, hake, and other fish that residents pull from the ocean essentially poisonous, heaping economic pressure on a region with tens of thousands of artisanal fishermen.
In one instance, protesters took over a principal access ramp to the island of Chiloé.
The government has offered to pay each affected family 100,000 pesos ($151) each in compensation, an amount fishermen have widely rejected as insufficient.