More than 400 dolphin corpses have mysteriously washed up on beaches in northern Peru.
Authorities are so far baffled as to the cause of the incident, while samples of the animals remains have been sent off for autopsies.
The mammals' remains were found on beaches stretching across the northern departments of Piura and Lambayeque, said Peruvian Sea Institute (IMARPE) official Jaime de la Cruz in Chiclayo.
Authorities failed to establish the cause of the 870 deaths in 2012 after autopsy results proves inconclusive.
The surge in deaths have sparked concern from experts, while some local media reports have speculated that toxic algae could have led to the deaths.
Yuri Hooker, director of the marine biology unit at Cayetano Heredia University, told The Associated Press that in other parts of the world dolphin deaths are generally caused by environmental contamination when the sea mammals eat fish or other smaller species filled with toxins. Others can die after ingesting discarded plastic floating in the sea, he added.
But Carlos Yaipen, a marine veterinarian at the NGO Sea Animal Conservation Scientific Group (ORCA) said if the death were down to what the dolphins had ingested, then humans would have been affected as well when they ate sea animals from the area.
Mr Yaipen said he wondered if nearby acoustic "impact" could have killed the dolphins, with oil companies doing exploratory drilling in the area.