Most of the time, when rodents make themselves known in New York, they’re not exactly celebrated—Pizza Rat notwithstanding. But when a beaver appeared in the Bronx in 2007, biologists were thrilled. The semiaquatic rodent, once incredibly populous in the area, had disappeared for two centuries, the victim of overzealous trappers and unwelcoming aquatic conditions in the Bronx River.

The river was indeed in a state of disgrace, with raw sewage being emptied directly into it, among other things. A sewer pipe was built to solve that problem in 1908. A larger cleanup was attempted in the '70s, but the biggest action took place in 2001, when the Bronx River Alliance formed to help transform the area. Their efforts, combined with the efforts of citizens and city government, not to mention $14.6 million in federal funding, finally helped restore the river. Just to start with, nearly 15,000 tires were pulled from its depths.

Just six years later, the hard work began to pay off when residents reported seeing a beaver in the river, a sign that the environment was habitable again. At first, biologists assumed the sightings were actually of muskrats, which look similar and are much more common. But upon further investigation, gnawed tree stumps and a 12-foot lodge made of twigs and mud seemed to verify the claims—and video evidence later cemented them.

The NYC transplant was named Jose after U.S. Representative José Serrano, who was a big player in helping to rejuvenate the river. But the happy ending gets even better—in 2010, the beaver population doubled when Jose was joined by a pal. Though a Bronx Zoo contest to name Jose's friend resulted in the name “Justin Beaver,” some people thought they had spotted signs that Justin was really female.

Will there eventually be a whole beaver family celebrating the newly clean Bronx River? Maybe—in fact, some researchers say there have already been signs that Jose and Justin(e) had expanded the family. If so, biologists will really have something to celebrate: A beaver colony hasn’t existed in New York City area “since Times Square was still farmland.”

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