Filmed in 1976 but not released until 1978.

The film was made and released about 115 years after its source novel of the same name by Charles Kingsley had been first published in its entirety in 1863.

Most modern editions of the book have an inscription on the copyright page that reads, "A number of references that would have little meaning or purpose for the children of today have been omitted from this edition, which is, however, in all other respects exactly as Charles Kingsley wrote it." It was put there by the editors of an edition during the 1940s.

Charles Kingsley wrote "The Water Babies" book for his son, it being a children's fairytale novel, in the vein of Charles Dickens and a part satire supporting Charles Darwin's "The Origin of the Species".

Though many of the source children's' novel's story elements were incorporated into this feature film version, the picture somewhat deviated from the original book by adding the sub-plot with the shark and kraken.

Samantha Gates, the girl who plays Elly, is the nude girl in the artwork for Led Zeppelin's album 'Houses of the Holy'. She is also the model in Hajime Sawatari's book "Alice", from 1973.

Many of the filming locations were places where James Mason had played as a child.

The full title of the movie's source book was "The Water-Babies, A Fairy Tale for a Land Baby".

Tommy Pender and Samantha Gates both receive "introducing" credits

One of a small batch of live-action animated movies made and released during the mid late 1970s, others being Pete's Dragon (1977) and Dot and the Kangaroo (1977).

Final film directed by Lionel Jeffries.

The movie's plot is summarized in a title card during the opening credits which state that the film is "A Story of a Little Chimney Sweep in the year 1850".

Charles Kingsley's "Water Babies" story was adapted into a radio series for the first time, for the BBC, in 1998.

In 2003, the film's source "Water Babies" book was produced on the stage for the first time as a straight play, adapted by Jason Carr and Gary Yershon.

"The Water Babies" had been previously adapted for musical theatre in 1902 at London's Garrick Theatre.

The last British animated film to have the animal vocals supplied by Clarence Nash, although he did appear in other animated films doing so until his death in 1985 just five months before the release of his last feature The Black Cauldron (1985) from Walt Disney Animation Studios. Starting with Watership Down (1978), the animal vocals will now be supplied by Frank Welker in future British animated films and other animated films in English worldwide.

Mr. Grimes and Mr. Masterman's fate is not entirely clear near the end of the film. They are obviously caught, but whether or not they are arrested, sent to jail or sentenced to death is never explained.