It was during production of this story that Peter Davison and Janet Fielding announced their departures from the series. John Nathan-Turner had offered Davison a fourth season in his role but, reportedly advised by Patrick Troughton, Davison chose to limit his time in the role to three seasons to avoid typecasting (the unwritten "Troughton Rule")
This was the first appearance of the Silurians since Doctor Who and the Silurians: Episode 7 (1970) and the Sea Devils since The Sea Devils: Episode Six (1972), both with the Third Doctor Jon Pertwee.
Though it was thought for a long time that Peter Davison performed his own stunt of flipping into the water tank, he admitted on the DVD commentaries that it was actually performed by the stunt coordinator.
Early in the production of the story, Prime Minister Margaret Thatcher announced a Parliamentary election. This created a sudden demand for BBC studio space, and as a result the production schedule for the story unexpectedly lost two weeks. Production was completed, but many signs of hurried production are evident. Many scenes had little or no rehearsal, and many scenes received only one take. Perhaps the biggest problem came with the Myrka costume. It was completed only an hour or so before it was scheduled to be used, so that the two puppeteers inside could not be fitted and had no time to rehearse in it. The costume smelled strongly of paint and adhesive, which one puppeteer said made him feel like he was sniffing glue. The paint on the costume had not dried by the time filming started, and tended to rub off on the sets and other costumes, as can be spotted in several scenes.
The characters of Doctor Solow and Preston were at first male, but Pennant Roberts charged their gender.