For decades, the beleaguered Bronx River has been known more for the things found floating on it, rather than for anything actually living in its waters. But now the city and environmentalists are working to reintroduce some fish to the river. NY1's Roger Clark filed the following report:

A cheer for some of the Bronx's newest residents. Alewife herring, trucked in from a Connecticut stream, are being introduced to the Bronx River, with the hope that they will reproduce. 

"They're mature and they are ready to spawn. They are eager to have their babies," says Marit Larson, the chief of natural resources with NYC Parks.

And it is hoped that those babies will eventually follow their parents out to sea, returning in four years to spawn.

It's a cycle that's easier said than done, since the building of dams on many rivers along the East Coast has stymied their passage, the Bronx River no exception. 

"Fish that have been wanting to come up the river and get to the fresh water stretches to have their babies have just been blocked," says Maggie Greenfield, executive director of Bronx River Alliance. 

Alewife fish can't get very high out of the water, so they need a little bit of assistance to get over dams like the ones on the Bronx River. That's why a fish ladder has been built to help them.

The contraption, installed last year, allows the alewife to get to the next level, migrating upstream to spawn. 

The effort to re-establish a breeding population here comes at a time when the Bronx River is at its cleanest in generations, thanks to volunteer efforts and clean-water laws. 

"With the water quality and really decades of concern that the community has put to the river, we know that the fish that are going to be born here, hopefully this spring in a few weeks, and are going to mature over the summer, are going to ha e the water quality they need to come back to," Larson says. 

"Bronx River was once a place where parents told their kids not to go anywhere near it," Greenfield says. "And now it's a place where thousands of kids come out every year to canoe the river. To learn from the river." 

And reintroducing the herring to the river creates an amazing opportunity for environmental education in the Bronx - plus to find out about other residents too. 

"American eels, we have birds, we have beaver on the river, which a lot of people don't know about. We are working to bring back oysters at the mouth of the river," Greenfield says.

And now, herring, returning to the city's largest fresh water river.