Over 3,000 dead dolphins have washed up on beaches in Peru since January 2012. 615 dead dolphins were found along a 135-kilometer stretch of coastline. The massive dolphin die-off is among the largest ever reported worldwide.

The strandings, which began in January, are a marine mystery that may never be unraveled. Experts say the causes could be acoustic impact from testing for oil or perhaps an unknown virus or other pathogen.