Goofs

In the beginning, when Jess' dad is chasing and gaining on the mermaid, the camera shows her head above the water and her back facing the boat, moving away from him. In the very next shot, less than a second later, she's suddenly on her back and not moving. She's smiling up at him instead.

The movie is titled "The Thirteenth Year", however, the time-line is inconsistent. When Cody is introduced, he's very clearly an infant, not a newborn, yet in the time-skip the words "13 years later" appear on the screen, implying that Cody would actually be several months older than 13. Also, the year after his 13th birthday would be his fourteenth year, not thirteenth.