The mermaid tails were six feet long and weighed over fifty pounds. According to Agnieszka Smoczynska, they were designed to look "repulsive" and different from depictions like Splash (1983) or H2O: Just Add Water (2006).
The characters of Silver and Golden were patterned after songwriters Barbara Wronska and Zuzanna Wronska.
The director said she and the producers originally thought because the twin sister mermaid characters were in their teens, maybe teenage actors should play the roles. But after awhile, she realized it's not possible for a teenager to act such very, very hard roles. They ended up auditioning over 2,000 girls until they found Marta Mazurek first and then Michalina Olszanska.
Based on Hans Christian Andersen's fairy tale "The Little Mermaid", published in 1837.
This film is part of the Criterion Collection, spine #896.