The Thirteenth Year (1999) is an American fantasy comedy, a Disney Channel Original Movie.

Cody Griffin (Chez Starbuck) is an adopted teenager. He was left with Whit (Dave Coulier) and Sharon Griffin (Lisa Stahl Sullivan) as a baby and he grows up to be a great swimmer and a popular student.

After his 13th birthday, Cody begins to feel strange. He gets scales and fins, and eventually his clever friend, Jess Wheatley (Justin Jon Ross) runs some tests and concludes that Cody is turning into a merman.

It is Jess, too, who works out a way for Cody to meet his mermaid mother (Stephanie Chantel Durelli).