Their Christmas Day did not go as planned.
About 70 people were injured Wednesday when a swarm of carnivorous fish attacked at a beach near the city of Rosario, on the Parana River, Argentina's state-run Telam news agency reported.
It described the fish as a relative of the piranha.
No one was killed.
But swimmers suffered various injuries, including a 7-year-old girl who lost a part of one of her pinky fingers, Telam said.
Ricardo Biasatti, sub secretary of Natural Resources for the province of Santa Fe, described the incident to the agency as "isolated and insignificant," when the size of the river is taken into consideration.
Julian Aguilar, president of a local fisherman's group, also downplayed it, saying the likelihood of such an event happening again was low, as attacks by this type of fish on humans are "occasional."
The area is a popular swimming spot this time of year in Argentina, where it is summer.