The eruption of a Tonga volcano sent "violent" waves across the Pacific and caused a boat loading oil about 6,600 miles away to topple, spilling thousands of barrels into Peruvian waters.
Dozens of fishermen have protested outside Peru's main oil refinery, La Pampilla, which processes around 117,000 barrels a day and is managed by Spanish company Repsol.
An Italian-flagged ship was loading the oil into La Pampilla when strong waves moved the boat and caused it to spill its cargo into the ocean.
Repsol said on Sunday it was caused by "the violence of the waves".
Three people have died in Tonga, including a British national, and most of the homes on its smaller islands been "completely destroyed" by the tsunami that followed Saturday's undersea volcanic eruption.
In Peru, two people drowned off a beach and there were reports of minor damage from New Zealand to Santa Cruz, California.
Peru's environment minister, Ruben Ramirez, told reporters an estimated 6,000 barrels of oil were spilled in the area, which is rich in marine biodiversity.
On Cavero beach, northwest of the facility, the waves covered the sand with a shiny black liquid, and small dead crustaceans were visible.
Fifty workers from companies that work for Repsol removed the oil-stained sand with shovels while workers dressed in white suits collected the spilled oil with plastic bottles cut in half.
Jose Llacuachaqui, another local fisherman leader, who was watching the clean-up, said the workers were collecting the oil that had reached the sand, but not the crude that was in the seawater.
"That is preying, killing, all the eggs, all the marine species," he said.
Protesters demanded to speak with representatives from the refinery but were largely ignored.
"There is a massacre of all the hydrobiological biodiversity," said Roberto Espinoza, leader of the local fishermen.
"In the midst of a pandemic, having the sea that feeds us, for not having a contingency plan, they have just destroyed a base of biodiversity."
Juan Carlos Riveros, biologist and scientific director in Peru of Oceana - an organisation dedicated to protecting the world's oceans - said that the species most affected by the spill included guano birds, seagulls, terns, sea lions, and dolphins.
"The spill also affects the main source of work for artisanal fishermen, since access to their traditional fishing areas is restricted or the target species become contaminated or die," Mr Riveros said.
"In the short term, mistrust is generated about the quality and the consumption of fishing is discouraged, with which prices fall and income is reduced."
Peru's environmental assessment and enforcement agency estimates 18,000 square metres of beach on Peru's Pacific coast have been affected by the spill.