In the state of Colorado you can only own piranhas if you have a permit. The whole reason that is required, and some states even have outlawed the fish completely, is because people were buying the predator fish and dumping them into lakes and streams. Did someone do that in Fort Collins? 

Piranhas are a deep-bodied South American freshwater fish that have very sharp teeth that are used to tear flesh from prey. They have a reputation as a fearsome predator. If you have never seen a piranha eating a hot dog, YouTube it!

Now imagine what these fish would do to other fish in local lakes, small dogs, or even a finger or toe of someone swimming in a lake... OUCH!

That is why Pedro Linsenmeyer and his son saved the fish they caught this week out of Sheldon Lake at City Park in Fort Collins. The Coloradoan did a story about the man and his son with pictures of the fish that looks just like a piranha. But experts say the fish is more likely a South American fish known as a pacu, which is a close cousin to the piranha. The fish is known as the “vegetarian” piranha, and the two can be told apart by their teeth. While piranhas have pointy teeth, pacus have squared-off teeth.

So the short answer to the question, "Are There Piranhas in Fort Collins' City Park Lake?," is yes, “vegetarian” piranhas known as pacus.