The rare greenback cutthroat trout lives in just one river in Colorado according to a new study.
The cutthroat trout, Colorado's state fish, now survives in just one 4-mile stretch of water southwest of Colorado Springs.
Researchers from the US and Australia used DNA samples from specimens of the trout that were pickled in ethanol 150 years ago and then compared it to the genes of today's populations, said the New York Times.
The study not only compared the genes of past and present but also examined more than 40,000 stocking records.
Restocking efforts in the area occurred during the last 150 years and saw 750 million varieties of trout put back into nearby waters.
More from GlobalPost: Thousands of fish die in Midwest due to heat
After DNA research was complete, the study authors found that the greenback cutthroat were so few that the remaining fish lived in just a small stretch of river.
"We've known for some time that the trout in Bear Creek were unique," said Doug Krieger, senior aquatic biologist for Colorado Parks and Wildlife, reported the Denver Post.
"But we didn't realize they were the only surviving greenback."
The discovery has prompted a flurry of efforts to preserve the fish, yet the Fish and Wildlife Service told the New York Times that it did not plan to take immediate action.
The fish's status would also not be changed from threatened to endangered until a more thorough scientific investigation was conducted.
The study was published Monday in the journal Molecular Ecology.