Turtles come ashore at the Ostional Wildlife Refuge in Guancaste, Costa Rica.

Tourists swarming a wildlife refuge in Costa Rica have disrupted the nesting of numerous sea turtles.

Hundreds of tourists stood in the way of the olive ridley turtles at the Ostional Wildlife Refuge in Guancaste, causing many of them to return to the sea without laying their eggs, the Union of Workers of the Ministry of Environment and Energy reported on its Facebook page.

Tourists touched turtles, stood atop their nests, took pictures with a flash camera, and even placed children on top of turtles to take photos, the organisation said.

FACEBOOK Tourists get close to the turtles coming ashore.

"So many people were on the beach that some turtles returned without completing the nesting process," Leonel Delgado, secretary of the union, told La Nacion. "That certainly is a negative impact."

Nearly every month there are mass turtle arrivals — known as arribadas, Spanish for "arrival by sea" — at the wildlife refuge, but September and October are normally the peak months of the season.

This year the September 6 arribadas fell on a weekend, and the weather was unusually fine, leading to the higher-than-normal crowds.

FACEBOOK A woman walks among the olive ridley turtles coming ashore.

Costa Rican authorities plan to meet to make sure that in future people only access the beach as they are supposed to — with a licensed tour guide.

Olive ridley sea turtles have an endangered statuus of "vulnerable".

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