Nadya Vessey lost her legs below the knees as a child and recently had a prosthetic mermaid tail made for her by director Peter Jackson's Weta Workshop. Fascinating, inspiring, and a just plain beautiful idea, Vessey's tail became a reality when Jackson offered to donate the labor if she could cover the cost of the materials, which she did with a grant.
There's a second video on YouTube showing Vessey swimming in the ocean, but I'm not sure where it comes from - it has a soundtrack added that features a song most people looking for an uplifting mermaid experience will find offensive, and shouldn't be played for kids.