Eighty Eastern Hellbender salamanders, Blue River's slimy unofficial mascot, were released into a secluded part of the river near Harrison Springs last week after spending four years in a research laboratory at Purdue University.
The odd-looking creatures can only be found in the Blue River watershed in Indiana.
Historically, the hellbender had a larger range, but the population dropped drastically due to pollution among other factors.
Blue River's cleanliness, cool temperature and steep grade provides a compatible environment for hellbenders.
But, the salamanders' reproduction has all but ceased in the last couple of years, according to Purdue's Help the Hellbender officials, who estimate there were only a few hundred left in the river before last Wednesday's release.
They've become so sparse the males have a hard time locating females, Erin Kenison, a Ph.D. student said just prior to the release.
Besides pollution, officials said the decline could be due to bank erosion and sediment entering the stream, causing cavities to fill in where hellbenders may have previously been located.
Hellbender eggs were taken from Blue River and reared at Purdue. Kenison has been the happy caretaker of the hellbenders for the last four years.
Part of Kenison's studies included a project to provide moving water, variable currents, for half of the salamanders in captivity to determine if those animals will be better suited for the wild as opposed to those reared in more stagnant, normal captivity conditions.
"We'll see if this form of conditioning will lend a hand, increase survival in the wild," she said. "They do seem to be better swimmers. That's what I've seen in the lab."
The salamanders, which were about a foot in length, were put into soft release cages for a few days before being completely turned loose.
"We're not just taking the buckets and dumping them in the river," Nick Burgmeier, research biologist and Extension wildlife specialist at Purdue, said.
He said all of the released hellbenders have surgically-implanted trackers so they can monitor their movements throughout the river.
It is not yet clear how many of the released salamanders are male or female, Kenison said, because they can only identify gender during breeding season.
Bob Sawtelle, O'Bannon Woods State Park manger, who shuttled folks to the release site, said they've partnered with Purdue researchers regarding hellbenders for decades.
He said he remembered in the 1980s when hellbenders could be easily found under rocks in the river.
Hellbenders, which eat mainly crayfish and other small fish, can grow to nearly 30 inches long.
The salamanders have working lungs and absorb oxygen from the water through capillaries of their side frills.
The Duke Energy Foundation funded a grant of more than $9,600 to Purdue for hellbender conservation last year.
"The funds were used for outreach and educational materials for the public in Southern Indiana as well as captive propagation equipment," Lisa Brones Huber, Duke Energy's government and community relations manager, said. "Duke Energy is committed to environmental stewardship and supports conservation efforts such as the captive propagation of the Eastern Hellbender and promoting environmental education."