"The FIN" started as a one-off example to restore a veteran amputee’s drive to go back into the water. Now, it’s becoming a tool that is delivering new hope and restoring aquatic mobility for lower-limb amputees.

Last year, Dr. Todd Goldstein’s 3-D printing lab of Northwell Health created a new lower-limb prosthetic to be used for swimming, called "The FIN."

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“The FIN came about as a way for Northwell to give back to our veteran community,” Goldstein told Fox News. “But as we were working through the progress of making a one-off custom piece for one of our veterans, it looked like it could work for other amputees.”

One of those amputees is NYPD Lieutenant Seamus Doherty, who lost his lower leg in 2002 in a motorcycle accident.

“Immediately after the accident, my leg was severed below the knee, so it was completely gone,” Doherty said. “It took me a year to get back on my feet and to get fitted for my original prosthetic.”

Doherty did not let his prosthetic deter him from advancing his career – he’s been promoted to sergeant, lieutenant and lieutenant commander since his accident – but he felt the limitations when it came to his young son.

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“I think the one main thing that was missing with the prosthetic that I had previously was the ability to freely go in and out of the water without the fear of destroying it, since they’re very expensive,” he said. “My son loves the beach and I wasn’t able to do everything I wanted with him in the prosthetic.”

Dr. Ona Bloom, a professor at the Feinstein Institutes for Medical Research at Northwell Health, explained to Fox News how the FIN confronted the problems of typical prosthetics.

“The FIN is printed at a lower cost than traditional swim prosthetics and has some design features such as a non-slip sole that is optimized for use on wet surfaces, and a flexible ankle hinge that fits over an individual's typical socket,” Bloom said. “That means it can easily be used to transition between swimming and other activities of daily living without requiring the user to switch prostheses.”

Goldstein said 3-D printing technology allows his team to print patient-specific measurements quickly with functionality.

“With 3-D printing in 3-D design, we can scale everything up and change the design pretty rapidly,” Goldstein said.

Thanks to the FIN, Doherty is now able to freely take part in the aquatic activities that he loves to share with his son.

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“I could actually take full part in the activities that he enjoyed," Doherty said. “I can go underwater with him and feel free that I can jump up and stand, and I have two feet if I need to grab him. It’s just so much more relaxed and so much more enjoyable.”

Emily DeCiccio is a reporter and video producer for Fox News Digital Originals. Tweet her @EmilyDeCiccio