Researchers trawling the lake on the California-Nevada border in a study to identify invasive fish species say they netted a goldfish that was nearly 1.5 feet long and weighed 4.2 pounds.
"During these surveys, we've found a nice corner where there's about 15 other goldfish," environmental scientist Sudeep Chandra of the University of Nevada, Reno, told LiveScience. "It's an indication that they were schooling and spawning."
Goldfish are considered an invasive species that could interfere with the lake's ecosystem, he said.
Aquarium dumping is introducing hardy, nonnative aquatic species to California waters that are a threat, researchers said.
Scientists say the fish must have come from aquariums because these species could not have ended up in these waters naturally.
"The invasion is resulting in the consumption of native species," Chandra said, adding the invasive fish also excrete nutrients that cause algal blooms that cloud Lake Tahoe's famously clear waters.
The size and aggressiveness of aquarium fish are the two main reasons people dump them, the researchers said.