This week, tourists in Ubarana, São Paulo had a nasty surprise during a day at the river. People swimming in the Rio Tietê in São Paulo state were attacked by piranhas. Luckily, no one was badly hurt and those who were bitten were treated at a nearby clinic.

According to the authorities, the piranhas attack every year. A barrier was built to try to keep the fish away from the artificial beach where people swim, but the fish manage to get around it.

Piranhas are omnivorous freshwater fish. They eat other fish, crustaceans, birds, small alligators, and sometimes even cattle. They sometimes even eat their own young. They are found in South American rivers, particularly in the Amazon, but even as far south as São Paulo.

Click here to watch a video about the incident.