There’s something strange going on near Lake Titicaca with its scrotum frogs (and it didn't happen on April 1).

At least 10,000 of these fat, wrinkly, and very rare frogs have mysteriously died in Peru. Thousands of the frogs were discovered floating in the river Coata by members of the Committee Against the Pollution of the Coata River. The river flows into Lake Titicaca, the highest navigable lake in the world, which straddles the border between Peru and Bolivia.

Although this die-off occurred on the Peruvian side of the lake, similar events have also been seen on the Bolivian side.

Sometimes referred to as the Titicaca Water Frog, the frog is only found in the waters in and around Lake Titicaca. The IUCN Red List declares this species as “critically endangered” and it’s believed the highly fragmented populations are all in decline.

They received their nickname “Titicaca scrotum frog” from their characteristic skin folds. They might make them look silly, but they’re actually a highly specialized adaptation. The frogs are effectively able to remove oxygen from water through their skin, so these folds actually help to increase this amount by increasing the surface area.