Imagine a refreshing summertime swim in the Chesapeake Bay or one of its tributary rivahs. Suddenly you vomit blood while a mysterious new form of parasitic isopod chews up your intestines, kidneys and liver. You die quickly and painfully.

Such is the storyline behind “The Bay,” a new, low-budget docu-drama produced by Barry Levinson, the Hollywood director who gave us “Good Morning Vietnam.”

Touting its pro-green message, “The Bay” posits that too much pesticide runoff from too many suburban McMansions and too many hormones in the feces of mass-produced chickens on the Eastern Shore are mixing in tepid Chesapeake water to produce baffling, organ-eating parasites.

Disaster unfolds as Fourth of July festivities begin in Claridge, a mythical bayside town in Maryland that could just as well be Urbanna or Yorktown. While screaming celebrants start dropping, emergency lines are flooded. The Centers for Disease Control rush to town dressed in bunny suits. The government clamps down on all communication.

How real can this be? Not a lot. Last year the U.S. Geological Survey said that 70 percent of bay test sites had showed improvement for nitrogen and phosphorous over the long term and 40 percent of sites showed improvement for sediments. Streams feeding the bay, however, showed consistent problems. During summer months, oxygen-depleted “dead zones” have shown up, notably in the bay’s Virginia waters.

Curious plant and animal phenomena also have appeared. In the 1990s, widespread algal pfiesteria blooms killed millions of fish. About six years ago in the Potomac, the ugly snakehead fish showed up. It swims and walks on land.

Its science might be a stretch, but “The Bay” — which opened Nov. 2 — seems to be getting good reviews. The Baltimore Sun gives it three stars, not bad for a flick that Mother Jones magazine reports was shot in 18 days for $2 million. Levinson tells the magazine that his movie “isn’t easy to watch. It’s very creepy.”