TODAY   |  February 22, 2013

Lake Tahoe invaded by non-native giant goldfish

California’s Lake Tahoe is one of the country’s most beautiful and clearest lakes, but scientists are becoming alarmed that it may be threatened by warm-water giant goldfish that are thriving as the lake has gotten warmer over the past decades. NBC’s Kristen Dahlgren reports.

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>>> now to california where a very big and unusual problem is lurking in the waters of lake tahoe , joint gold fish .

>> no!

>> uh-uh heard me, giant gold fish . kristen dahlgren has the story.

>> reporter: ever wonder what it's like to be a big fish in a big pond ? these giant-sized gold fish know. they've invaded one of the country's most pristine bodies of water , lake tahoe .

>> not your average-sized gold fish .

>> warm water gold fish not native to lake tahoe . as the lakes have gotten warmer, scientists say the gold fish are thriving. oversized creatures measuring a foot and a half long, weigh in at four pounds. substantially larger than typical pets in a fish bowl and it's their size that shocked researchers from the university of nevada , reno.

>> we know we have a giant gold fish . the question now is how long has it been there and how many others are there in the lake?

>> reporter: gold fish are carp that eat almost anything, potentially throwing off the lake's ecosystem and threatening other native fish. how did gold fish get in to lake tahoe ? the presumed culprit, people dumping aquariums along the shoreline.

>> there are a lot of people that still don't understand that it seems like a very minor thing can add up to major ecologic and economic consequences.

>> reporter: no longer a little fish , the big gold fish are now causing big problems in lake tahoe . for "today," kristen dahlgren, nbc news, los angeles .