Identity, the desire for independence, and breaking down cultural barriers between different "worlds" (land and sea).
While many movies feature these mythical creatures, two primary versions dominate modern interest:
All The Barbie Movies * Barbie in the Nutcracker. 2001. 1h 16m. ... * Barbie as Rapunzel. 2002. 1h 24m. ... * Barbie of Swan Lake.
For those who prefer a darker twist, this Russian horror film (original title: Rusalka: Ozero myortvykh ) offers a supernatural take on the myth.