Godzilla vs. Hedorah (1971) on Netflix

By this time, Gojira, defender of the Earth, has become a national phenomenon, akin to the Loch Ness Monster, especially with children, ingrained into the Japanese conciousness. However, the Japanese people still don't realize that destroying the earth will summon the millennias-old protector. A young boy finds a dangerous monster that thrives on toxic waste that he names Hedorâ, a pun on the Japanese word for sludge, "hedoro." In his dreams, he wishes for Gojira to defeat Hedorâ and, hopefully, persuade people to stop polluting the earth. Gojira, coincidentally, fights the monster because of the destruction to the environment.