Hundreds of mud-covered Carnival revellers paraded in the sleepy seaside town of Paraty in south-eastern Brazil on Saturday, a decades-old tradition that has grown ever larger since its first edition nearly 40 years ago.

Joyous partygoers threw themselves into the silty shallows in front of one Paraty beach, emerging grey from the sludge.

They danced on the beach and grunted cavemen chants – “Uga! Uga!” – before marching along the sand.

“It’s the best bloco. It’s not often that you can get muddy and go around dancing and singing. It’s very gooey, it’s sticky and it stinks, but it’s very good,” said Thais Beazussi, 20, who lives almost two hours away by car, but makes the annual trip.

Carnival in Brazil is a combination of world-famous parades by samba schools who spend all year around preparing and eccentric street parties, each with their own theme, aesthetic or musical style.

The mud party’s tradition dates to 1986, according to Paraty’s tourism website.

Friends were playing in the mangroves at Jabaquara Beach, and realised they weren’t recognisable.

They went strolling into the city’s historic centre and caused a stir.

The next year, a group lathered themselves up with mud to present themselves as a prehistoric tribe for Carnival. They carried skulls, vines and bones as they uttered their chants, the site said.

And so the mud party was born. And in the years since, it has become a beloved tradition.

Its growth has forced organisers and Paraty’s tourist office to promote awareness ahead of the event regarding the importance of not dirtying the city’s colorful walls, cars or onlookers.