Peruvian authorities are currently investigating the circumstances under which 500 sea lions died and washed ashore in the northern part of the country’s coastline. Authorities are currently cleaning up the beaches, as the corpses could become health hazards.

The hundreds of corpses were discovered over the weekend on Anconcillo beach in Peru’s northern department of Ancash, according to the Peruvian newspaper El Comercio. Agents of the Police Department of Tourism and Environmental of Chimbote arrived on the scene to find the already decomposing bodies of the sea mammals.

The sea lions discovered are both young and mature mammals, but the remains are far too decomposed for a thorough investigation, according to officials. However, they will continue investigation into the cause of the mass deaths.

Cleaning crews, equipped with front loaders, have been cleaning up the beach.

According to the BBC, the local governor accused fishermen of poisoning the animals, but Peruvian police are also investigating other causes like disease and accidentally ingesting plastics.

Earlier this month around 187 dead sea lions washed up farther north on the coast of the department of Piura, according to Peru21. Police are also investigating that mass death but have not released any information.

The BBC adds that in 2012, hundreds of dolphins washed ashore. Environmental groups blamed blasts from oil exploration, but the government’s marine agency said natural causes were to blame.

Check out tweets regarding the recent discovery of sea lion corpses below: