The woman who was attacked by a crocodile near Puerto Escondido, Oaxaca, on Sunday was swimming in an area known to be a danger zone for its large crocodile population.

Backpackers Melissa Laurie, 28, and twin sister Georgia Laurie, from Berkshire, UK, and 23 other tourists went on a boat tour to Puerto Suelo beach near Manialtepec Lagoon, reported the local news portal Ecos del Pacífico.

A number of the tourists diverged from the group and walked across the beach to the mouth of the lagoon where they entered the water.

According to witnesses, the sisters swam through the river which connects the lagoon to the beach, advancing more than 300 meters against the current. They tired, and chose to swim to shore over a grassy area without noticing that  there was a crocodile within.

Melissa Laurie was attacked by the reptile and dragged underwater. Her sister fought it off, punching it until it let go.

Tour guide Arturo Venegas, who was in the vicinity, described the area. “We know that it’s a place with a lot of [crocodiles]. We knew that the two girls … got in in the part of the river where there is a lot of undergrowth, and that was where the girl was attacked by the animal,” he said.

Guillermo Silva, a local public safety officer, took part in an investigation to reconfigure the events. He attested to the dangers of swimming in the area, and explained his theory as to why the crocodile attacked. “This is not an area for tourism, it’s an area that nests crocodiles above all else. It is rainy season and that makes it even easier for crocodiles to nest. Where the accident happened there is a probability of nesting crocodiles, and a female could have been defending her eggs,” he said.

Melissa Laurie is currently in an induced coma because of fears of infection, while Georgia is recovering from her injuries.

The sisters are in the midst of a backpacking tour around the world. They left the UK in March and had planned to return home in November.

CORRECTION: Information about the boat tour and the prevalence of crocodiles was incorrect in the previous version of this story. 

With reports from Ecos del Pacífico