Back in 2000, an art student at Michigan State University jokingly scribbled "Monkey Day" on a friend's calendar under December 14. Fifteen years later (and a lot of time spent messing around in simian suits), World Monkey Day is marked across the globe. So what's it all about? Well, aside from a "a chance to scream like a monkey and celebrate your simian attributes", December 14 is about raising awareness for the planet's monkey species.

To celebrate, we're bringing you this awesome footage of endangered toque macaques cooling off in Sri Lanka’s Gem River, filmed by cameraman and wildlife biologist Alex Barczkowski.

Toque macaques (Macaca sinica) live in highly structured social hierarchies with as many as 40 individuals in a single troop. They actively swim, dive and play in water (something that other monkey species have been known to do in order to cool off in the heat of the day). Although they are found all over Sri Lanka, toque macaque populations are shrinking and have declined by more than 50% in the last 40 years due to habitat loss, persecution and exploitation for the pet trade. 

Header image: Joanne Goldby