Many giant goldfish like this one have been found in Lake Tahoe. Source
New research into invasive species that plague Lake Tahoe has revealed a school of giant goldfish that appear to have been dumped by their owners. One of the goldfish scooped up was 1.5 feet long and weighed 4.2 pounds, a far cry from a child's pet. It is a common misconception that goldfish are small animals. Oftentimes these fish are kept in small tanks and fed very little, but if a goldfish is kept in a large, warm, filtered tank and fed frequently, it can grow to an enormous size. This becomes a problem when goldfish are abandoned in the wild. These fish are hardy and will push out native fish if they are left alone. LiveScience has a very good article on this.