Most of the characters were written with the actors in mind. Octavia Spencer said her character was reminiscent of a collaboration between her roles in The Help (2011) and Hidden Figures (2016), and that she "would have played the desk if Guillermo del Toro had asked me to".
As this is released in theaters the same year as Maudie (2016), it marks the first time Sally Hawkins has been the lead in two theatrical releases within the same year. In both films, she portrays a woman with a disability; In "Maudie" her character suffers from a result of juvenile rheumatoid arthritis, and in "Shape of Water" her character has a speech impediment.
Doug Jones has said about The Shape of Water (2017): "...I played a creature in it, in a full rubber, you know, transformation from head to toe. ... Sally Hawkins is like the lead of the movie, and the one I had most of my scenes with."
A series of photos depicting artist James Jean's progress on the poster artwork can be found on his Instagram page. On two such photographs, reference photos of the creature can be seen in the corner, presumably unreleased stills from the actual movie.
The trivia item below may give away important plot points.
One of the Octavia Spencer's favorite things about the screenplay was the fact that by letting the main couple be mute, most of the dialogue comes from a black woman and a closeted gay man. In real life, they would both have experienced suppression during the 1960s setting of the film.