Scott Porter remembers the last time he felt completely well. It was a warm, clear day with sparkling blue skies in June 2010. A deep-sea diver and marine biologist, he was taking a TV news crew out on a 30-foot catamaran to one of his favorite spots in the Gulf of Mexico, a coral reef growing on an abandoned oil platform at Main Pass 311. It lies about 40 miles north of the Deepwater Horizon drilling rig, which had exploded six weeks earlier. The rig’s severely damaged wellhead a mile below the surface was still gushing thousands of barrels of oil a day—and ongoing coverage of the accident continued to generate headlines. Federal officials had assured Porter that the water around the reef was safe, but the acrid smell of crude permeated the air. The minute he plunged into the murky seas, he found himself immersed in a 40-foot-thick mucous plume of oil and chemical dispersants.
“At midday, it’s normally light enough to read a book even 60 feet below,” Porter says. “But the oil blocked out so much sunlight, I couldn’t read my gauges.” Porter recalled the incident while picking over heaping platters of boiled shrimp and crawfish, specialties at Big Al’s, a popular Cajun-style eatery in Houma, about 60 miles southwest of New Orleans—and in the heart of Louisiana oil country. Porter, who consults for oil companies and environmental groups, lives nearby in this bustling metropolis of 30,000. It’s a starting point for fishermen headed to the Gulf and for oil crews that bunk in chain hotels crowded along the town’s main drag before heading out to the rigs for two- to three-week stints.
Porter has spent a lot of time underwater—more than 6,000 dives over a 20-year career, he estimates—but that dive was different. “I felt like I was marinating in a vat of industrial solvents,” scowls the 49-year-old native of the Texarkana twin cities. When he got home that night, he developed a terribly itchy skin rash. He felt as if his lungs were seared by fire, with an intense burning sensation in his chest that he knew from experience was chemical pneumonia, caused by inhaling harsh solvents. But he kept diving. And after each subsequent dive, he developed more ailments—chest colds, a burning throat, pounding migraines, bone-deep lethargy and nausea. 
Many other Gulf residents are stricken with some of the same odd symptoms—and more. They include migraines, skin rashes, bloody diarrhea, bouts of pneumonia, nausea, seizures, muscle cramps, profound depression and anxiety, severe mental fuzziness and even blackouts.