Yep, a ‘little’ goldfish… like the ones in your little aquarium, except somebody threw them in a lake and they grew up… AKA CARP!!!
They are aggressive, grow bigger than you think, and contribute to poor water quality when they uproot and disturb submerged vegetation while searching for insect larvae to eat. They also reduce water clarity and stir up bottom phosphorus-containing sediments, which contributes to algae blooms.
Are they that much of a problem???
Yes! HERE is an article from Popular Mechanics about dealing with invasive carp.
OBTW, they aren’t really that edible either. Oily and, as bottom feeders, tend to be ‘muddy’ flavored unless ‘cleaned out’ thoroughly in clear water.
FYI, Koi (the pretty fish in a lot of Japanese fish tanks/hotels/Hawaii are also carp!!!