Tomoyuki Tanaka, who produced the first 22 Godzilla films, was in the hospital during the time the film was made. Upon recovery and actually seeing the film, it is said that he told the director of the film he ruined the Godzilla series and that he would never direct at Toho again.
The movie starts out with a long shot of polluted water where Hedorah rises slowly, the title shows onscreen. Credits roll with shots of sludge and garbage floating past on the water mixed with images of a woman singing "Save the Earth" in Japanese. We then come to the home of the Yano family, consisting of Dr. Yano, a marine biologist, his wife, Toshie, and his son, Ken. A fisherman comes to their house with a large black-colored tadpole-esque fish. A friend of the Yano's, Ken, the Doctor, and the fisherman agree it couldn't be a tadpole for a few reasons (Size, area where it was found, color, etc.). The doctor asks where the fisherman caught it, and he said it was down where he normally went shrimping, saying it was strange he didn't get any. As the family and their friend are eating. a news report comes on about a large creature, similar to the fish they found, attacking two boats, destroying them. One theory put out was that it was a military weapon. A clear photo of the creature comes onscreen in the report. Ken exclaims it was the same as the fish the man brought earlier. They travel down to where the fish was caught, the doctor in scuba gear, the boy with a knife and pail. The doctor tells his son he'll be back in thirty minutes and dives in. Dr. Yano swims around for a while without finding anything other than garbage on the bottom of the water. As Ken cracks open oysters attached to the rocks in the water, finding nothing, the creature causes a wave to crash into him as it is swimming toward him. He holds his knife up in the air as it jumps above him, creating a large gash in its underbelly. It swims off, leaving Ken on the rocks, calling out to his father. The doctor soon sees the creature, it goes toward him and burns his face with acid. He is brought back home later on, having been treated for burns. In an interview with the press, they discuss the two creatures (as the one that attacked Ken and Dr. Yano was much smaller), Ken refers to them as "Hedorahs", however the name appears to catch on. They discuss how both of the Hedorahs were found in polluted water. Another news report states three more tankers were taken down by the larger of the two. A crude cartoon of a green-colored Hedorah drinking oil from the tankers among hundreds of dead fish is shown. In the background, smoke billows from several chimney stacks.
Classic Godzilla music plays momentarily on a picture of a sunset/sunrise as Godzilla slowly comes on-screen and roars. Various shots of polluted water appears again. Ken has a short monologue about nuclear fallout and waste being put into the sea as Godzilla sets fire to the sludge on the water (apparently for a report of some kind, as evidenced by his lines at the end).
- On a side note, this was the first - and only - time we see Godzilla fly. He uses his atomic breath as jet propulsion. Banno reportedly added the scene to provide a light moment in what is otherwise a fairly dark movie compared to many of those which preceded it.
- The Godzilla suit used predominantly in this film is the same "SoshingekiGoji" suit used for the last two films, Destroy All Monsters (1968) and All Monsters Attack(1969).
- Hedorah was portrayed by a man named Kengo Nakiyama, who, 13 years later, would play Godzilla himself in The Return of Godzilla (1984) and reprise the role for the remainder of the Heisei series films. (By that time he had changed his name to Kenpachiro Satsuma.) He also portrayed Gigan in both Godzilla vs. Gigan and Godzilla vs. Megalon, respectively.
- Hedorah is the last monster that Godzilla battles in the Showa series that acts independently and is not under the control of some other being.