Jason Thompson used to love fishing in the lake he can see from his window in Mayflower, Arkansas, but these days, when he throws a line out into the water, the lure he reels back is covered in a sour, stinking black tar, the skirt of the jig stuck uselessly together. When he brings the fingers that touched the line up to his nose, he gets a whiff of the same putrid stench that filled the air for weeks after the oil pipeline burst—the smell that still rises out of the ground every time it rains.

Thompson hasn’t been fishing much. Ever since Exxon Mobil’s Pegasus pipeline burst in March and spilled an estimated 210,000 gallons of Canadian heavy crude oil two miles from his house, he’s had headaches of preternatural intensity, so bad they wake him up in the middle of the night. He has nosebleeds, and hemorrhoids even though he’s only 36; there’s a rash on his neck that has only gotten worse in the eight months since the spill; and some days he feels so weak that he can hardly get out of bed. He estimates that he has lost almost 35 pounds since the rupture, falling from a fit 220 down to 185. When he went to see a doctor in April, he was told he has a mysterious spot on one lung—but he hasn’t been able to afford to go back.

Hundreds of people in this working-class town of 2,200 have complained of symptoms like Thompson’s. And their maladies—respiratory disorders, nausea, fatigue, nosebleeds, bowel issues, throbbing headaches—echo the ones that appeared in Marshall, Michigan, where an Enbridge Energy pipeline burst in 2010. The two pipelines were carrying the same kind of oil: a heavy crude, or bitumen, mined in the tar sands of Alberta, Canada, which is thicker and rawer than the oil extracted in the United States. This is also the oil that would flow in record quantities through the controversial Keystone XL pipeline, if President Barack Obama decides to approve it.

The Mayflower spill should alarm communities along Keystone’s proposed route. Experts believe it happened in part because the leaden crude from the Alberta tar sands erodes pipelines faster than the oil the U.S. is used to shipping: Bitumen is so thick, it has to be transported at higher pressures and temperatures, and it must be diluted with gas before it can flow, which can lead to violent pressure swings inside the pipeline. This new danger isn’t inspiring much caution in the energy industry, judging by the Associated Press's recent revelation that 300 spills have occurred in North Dakota alone in less than two years, and all were kept secret. On average, U.S. pipelines spilled over 3.1 million gallons a year between 2008 and 2012, according to the Pipeline & Hazardous Materials Safety Administration (PHMSA). As for the Keystone project, Public Citizen released a report this month documenting over 125 patches, dents, and other worrisome anomalies in its southern half.

Likewise, in a report released November 6, PHMSA found that Exxon knew it was gambling when it repurposed the 65-year-old pipeline, which stretches 858 miles from Illinois to the Gulf Coast in Texas, in 2006. (Built to carry lighter oil from south to north, it was converted to carry tar sands crude from north to south.) Tests the company performed before reversing the line “provided more than adequate information for the pipe to be considered susceptible to seam failure,” PHMSA chided, and yet, “The operator failed to establish a five-year reassessment interval” for the section that ultimately burst on March 29, 2013. PHMSA’s assessment may have been scathing, but the fine it proposed is barely a slap on the wrist: just $2.6 million, or .0003 percent of the company’s $7.8 billion profit in just the third quarter of 2013. In other words, Exxon took a calculated risk, and the residents of Mayflower are paying the price.