WARNING: CONTAINS GRAPHIC CONTENT
Pharmacy student Welida Vale de Menezes, 24, was cooling down with friends at Aramanai beach in the municipality of Itaituba, in the northern Brazilian state of Para, on 17 October.
She said others had already warned her about feeling something in the water, but she dipped her toe in anyway.
When the attack happened, Welida initially thought her toe had just been badly cut, but soon realised she was missing part of it.
She had to be taken to a local hospital by boat, later getting confirmation that she'd lost half of one of her toes.
Welida told local media: "I was sitting on the sand with my foot in the water. My friend had already warned me that he had felt something in the river and he took his feet out and left.
"I then felt something biting me. I ran my finger over it and I thought it was just cut. I didn't know it had ripped off a chunk of my toe."
After receiving treatment at hospital, Welida was discharged the same day.
She added: "The doctor told me that there was no way to stitch the entire wound, but I still got eight stitches.
"The parts that were not stitched will have to stay as an open wound while they heal."
Welida is still in a lot of pain, with estimates suggesting the wound will take 60 days to heal in total.
Even 20 days after the bite, she was unable to stand on the ground, and is only just starting to take her first steps with difficulty, with the aid of crutches.
She continued: "This could happen to anyone. I'm worried because there were lots of children in the same place as me.
"I couldn't imagine that a fish could rip off half of my toe and in that place, where it was busy.
"I hope my case serves as a warning and that people pay more attention. I don't wish this pain on anyone."
Saying she has no plans to return to the beach anytime soon, she added: "I don't have the courage to go anymore, no. Honestly, I can't risk it happening again."
While piranha attacks were once rare, they are becoming increasingly common at Aramanai beach.
In the past two months alone, six cases at the beach have been reported at the beach - including a man who had a chunk of the sole of his foot ripped off.
Authorities believe the rise in the number of cases may be due to locals throwing food in the river.