With "The Bay," Barry Levinson Makes Eco-Horror Roadside Attractions Jane McNeill as a resident of a town whose water supply is contaminated in "The Bay," directed by Barry Levinson. WHEN the villain of a horror film is an ax-wielding maniac, the doomed victims can at least beg for mercy. Reasoning with Freddy Krueger may not get you very far, but you can pray he has a conscience somewhere. What makes eco-horror films - from the 1954 sci-fi classic "Them!" to Steven Soderbergh's 2011 thriller "Contagion" - so terrifying is that the enemy is Mother Nature herself, and she is invariably merciless. Right on time for Halloween comes "The Bay," a biological thriller by the Oscar-winning director Barry Levinson that played at both the Toronto and New York film festivals this year and opens across the country on Friday. Set in a small Maryland town on Chesapeake Bay, the film, a work of fiction, takes a look at what happened on July 4, 2009, several weeks after toxic materials from a local salination plant were pumped into the drinking water. The film is narrated by a young, inexperienced journalist (Kether Donohue) who describes what happened during the town's Fourth of July festivities, when parasitic creatures that had burrowed inside unsuspecting townsfolk suddenly started to get hungry. Her video as well as surveillance and point-and-shoot footage taken by others on the day of the outbreak show a town in chaos as the critters aggressively and gruesomely eat their way through their human hosts. The conceit is that her footage was confiscated by the federal government as part of a cover-up. The idea behind "The Bay" began after Mr. Levinson was asked to direct a documentary about environmental crises facing Chesapeake Bay. After watching a 2009 "Frontline" broadcast on the topic he opted instead for a graphic fictional treatment. "I don't know that we pay attention to facts anymore," he said over lunch in New York recently. That the film takes a horror angle is a surprising departure for Mr. Levinson, who is known for more mainstream films like "Rain Man," "Good Morning, Vietnam" and "Diner." He shot his cautionary tale in South Carolina for just over $2 million with a cast of mostly unknown actors in a found-footage style, using more than 20 camera types, including Skype and iPhones. The flesh-eating creatures in "The Bay" were inspired by research conducted by Mr. Levinson and the screenwriter Michael Wallach into isopods, crustaceans that live on both land and in water, nip at people and can be parasitic (although they would never chomp off human body parts, as happens in "The Bay.") In other words, a perfect villain for an ecologically anxious age. One species of isopod "eats fish from the inside out, and eats the tongue," said Mr. Levinson. It grows to two and a half feet long in some cases. That's pretty scary stuff. Knowing an isopod is real, Mr. Levinson said, makes the film "more unsettling." "You show it to a test audience, and they don't know an isopod is real," he added. They think you made it up. It's like showing "Jaws" and no one knows there's any such thing as a shark. You say it's really in the water? That's scary. "The Bay" is the latest in a long line of films that pit man against natural forces run amok. In the 1950s, when the threat of nuclear annihilation began to cast its shadow, films like "Them!," about man-eating ants made monstrous by atomic testing, began to emerge. In the "60s Hitchcock rattled audiences with "The Birds." As the environmental movement gained steam in the "70s and "80s, a new wave of movies found threats throughout the natural world, from national parks ("Grizzly") to city sewers ("C.H.U.D."). More recently the genre has been preoccupied with microbial or unseen eco-terror, in movies like M. Night Shyamalan's 2008 film "The Happening," which turned the wind rustling through the trees into a killer, and Mr. Soderbergh's "Contagion," which tracked the global progression of a deadly virus. An eco-horror story essentially goes one of two ways, according to Michael Ridler, editor of the Canadian horror blog HorrorMovies.ca, who has written about the genre. The threat can exist in nature, like an insect or an earthquake. Mr. Ridler points to the film "Frozen" (2010), in which skiers battle bitterly cold conditions when they are stuck on a ski lift after hours. Mankind can also cause the destructive force, usually through hubristic means. In "Mimic" (1997), for example, genetically engineered insects breed in the New York subway system, creating "eco-horror of our own making," Mr. Ridler said. "We have to breathe the air and drink water," he continued. If you take one of those common elements, or put something into those elements, and make it the enemy, it becomes terrifying. As for the threats posited in "The Bay," "We certainly don't think the conditions described in the film are within the realm of possibility," said William C. Baker, president of the Chesapeake Bay Foundation, a conservation group. But they are a literary exaggeration of real issues that the Bay does confront. Mr. Baker said bacteria in polluted water can cause human health problems, including severe infections that mirror those depicted in "The Bay." Among the producers of "The Bay" are Jason Blum and Oren Peli, the same team behind the successful "Paranormal Activity" horror franchise. But beyond that pedigree "The Bay" - like many eco-horror films - could be as much an educational tool as a scream inducer. "If Barry Levinson's film can raise awareness about what could happen in the very worst of cases if pollution remains unchecked, then that will provide a great service," said Mr. Baker, who hasn't seen the movie. Saying he doesn't like films "where they seem too preachy," Mr. Levinson nonetheless sees "The Bay" as a chance for both entertainment and reflection. Sometimes when humans toy with nature "it ultimately creates the ills that come about," he said. We somehow think we can do whatever we want. There are warning signs all the time, and we still ignore it. We ignore and go along our way and hope everything's going to be fine.