Filming took place in the swamps of South Carolina, and this proved to be a fairly miserable experience. "It was during a ferociously hot summer with very, very high humidity, and there was a black caterpillar plague, so they were in the trees in big clumps and would drop down on your head and sting you."
Wes Craven was unaware of the Swamp Thing before being approached to direct because he had no access to comics while growing up. "They were forbidden by the church I was raised in." He found the comic book idea fascinating though, and after reading through the series he was ready to jump in fully.
Stuntman Anthony Cecere, who also did the Freddy burn in A Hora do Pesadelo (1984), "taught himself how to do it by trying various chemicals on himself around the family swimming pool and setting himself on fire."
Adrienne Barbeau's topless scene was shot and intended for use solely in the European release and therefore not included in the American cut. "It was one of those things of just gratuitous breast-ness," director Wes Craven said on the DVD commentary. While the PG cut teases a brief profile shot, Craven believed the full scene was the absolute definition of gratuitous. "When it first came out on DVD through MGM they released the European cut in the States," DVD commentary moderator Sean Clark said. "Once it was discovered, they immediately recalled it." According to Clark, MGM contacted Barbeau to see if she would just sign off on the mistake, but she refused, citing the terms of her contract.
The idea for A Hora do Pesadelo (1984) came to Wes Craven during production on this film, and he said that's the only positive that came out of it career-wise. He survived a few years on the paychecks from this and Benção Mortal (1981), but that quickly dried up. "I went through all the money I had saved, I lost my house, and I was literally selling my goods, and I think I borrowed from Sean S. Cunningham five grand to pay my taxes that year."