An aerial view of an oil sands mine near the town of Fort McMurray in Alberta Province, Canada. Mark Ralston/AFP/Getty Images

A new government inquiry into a wave of sickness in Alberta, Canada, suggests that residents’ conditions may be linked to Canada’s controversial oil sands developments. The inquiry also finds that area doctors may be afraid to speak out when patients suggest that the oil developments could be the cause of their health problems, according to the Edmonton Journal.

The survey of doctors was conducted by Dr. Margaret Sears, a toxicology expert hired by the Alberta Energy Regulator. Sears and other experts were tasked with analyzing the health effects of the oil sands operations in preparation for a 10-day government hearing to address residents’ health complaints around the Peace River oil sands, Canada’s third largest oil sands development.

For the past two years, since Canadian company Baytex Energy began drilling dozens of wells to extract oil-rich bitumen around Peace River, a remote and sparsely populated community in northern Alberta, residents have complained of, “powerful, gassy smells and symptoms including severe headaches, dizziness, sinus congestion, muscle spasms, popping ears, memory loss, numbness, constipation, diarrhea, vomiting, eye twitching and fatigue,” according to the Toronto Star.

Shell also owns wells in the area.

At issue are above-ground tanks used to heat bitumen, a rock formation largely comprised of carbon. The tanks have no lids, and residents say the overpowering smell has caused all sorts of health issues.

But when residents reported their symptoms to doctors in the area, physicians were reluctant to consider the oil sands as a reason for their illness, according to Sears’ investigation. In at least one instance, a patient was turned away after suggesting that their symptoms were due to oil developments.

“Communications with public health officials and medical professionals revealed a universal recognition that petrochemical emissions affect health; however, this was countered by a marked reluctance to speak out,” wrote Sears.

Sears concludes that doctors’ reluctance stems from a lack of information about environmental health — but also from a troubling history of perceived retribution for speaking out against oil developments in Canada.

In 2003, after Dr. John O’Conner sounded alarms over a cluster of a very rare cancer near an oil patch in Athabasca, staff at Canada’s health regulator Health Canada filed five complaints against O’Conner, which could have cost him his license. The move was widely seen as an attempt to dissuade him from speaking about the cancers.

Sears wrote in her report that doctors around Peace River referenced the case of Dr. O’Connor several times.

“Physicians are quite frankly afraid to diagnose health conditions linked to the oil and gas industry,” she wrote.

Baytex’s method of heating bitumen in above-ground tanks to extract oil is relatively unique among the Canada’s vast oil sands developments.

Oil from the sands is potentially worth hundreds of billions of dollars. The extraction and perceived lack of environmental regulation has had activists up in arms over the last few years. But Canada’s government says it sees the oil sands as necessary for sustaining the country’s economy.