Yeah, goldfish are a huge problem around the world. Even where I live, there's a wild pond a couple miles from me that is known to have goldfish in it. I was told that by someone about 15 years ago. One day I was in the area so I went over to check it out and sure enough, it did. Very disappointing. People do this with all sorts of animals, too. They just release them into the wild without any thought or care about what kind of damage it can do.
Best case scenario, the animals die quickly because they can't take care of themselves in a wild environment. Worst case scenario, the animals breed and become invasive. It's a lose-lose.