For over 60 years, the U.S. Navy used the small island of Vieques, Puerto Rico, as a bombing range and site for military-training exercises. Then the island got sick. Thousands of residents have alleged that the military’s activities caused illnesses. With a population around 9,000, Vieques is home to some of the highest sickness rates in the Caribbean. According to Cruz María Nazario, an epidemiologist at the University of Puerto Rico’s Graduate School of Public Health, people who live in Vieques are eight times more likely to die of cardiovascular disease and seven times more likely to die of diabetes than others in Puerto Rico, where the prevalence of those diseases rivals U.S. rates. Cancer rates on the island are higher than those in any other Puerto Rican municipality.The Navy eventually conceded to using heavy metals and toxic chemicals like depleted uranium and Agent Orange on the island, but denied any link between their presence and the health conditions of the people who live there. To this day, it is unclear what exactly caused the current conditions in Vieques. It’s a health crisis with a cause that’s almost impossible to prove: The government requires a particular standard of causal evidence before it will administer relief. Yet independent groups cannot necessarily provide that proof because the federal government still owns the land previously occupied by the military and controls access to it.Conflicting studies by local scientists and the U.S. government have offered different explanations for Vieques’s sickness. Until 1997, data on the matter was scarce. That year, Nazario and a nonprofit civic organization noticed a high incidence of cancer cases in Vieques and filed a public grievance against the Department of Health. Soon after, the agency published a study showing that the prevalence of cancer in Vieques was 27 percent higher than in the rest of Puerto Rico. “For the first time, the excess of cancer in Vieques was acknowledged,” said Jorge Colón, a chemistry professor at the University of Puerto Rico known for his work advising several grassroots organizations in Vieques. The study recommended that the Department of Health carry out a public-health assessment of environmental conditions on the island.The report went essentially unrecognized until waves of protests pressured the Clinton and Bush administrations to withdraw military presence from the island. While the Navy left Vieques from 2001 to 2003, the federal Agency for Toxic Substances and Disease Registry, or ATSDR, released reports that found no causal link between the high rates of sickness and decades of weapons use on the island. The government sought proof of cause as its evidentiary standard. In their evaluations, the ATSDR looked at four “exposure pathways”—air, seafood, soil, and water—and found them to have “no apparent public-health hazard.”Nazario and other local scientists questioned these findings. In particular, she criticized the agency for not conducting any direct epidemiological studies on Vieques’s population, relying on soil samples collected by the U.S. Navy, and barring scientists from conducting independent research. This sentiment was shared beyond the borders of Puerto Rico. At a congressional hearing in May 2010, the Yale University environmental-health professor John Wargo said the agency’s public-health assessments “contain serious flaws in scientific methods” and added that, in Vieques, ATSDR found that an “absence of evidence of contamination is sufficient to conclude the absence of significant health threat.” In other words, he argued, the federal agency used a lack of evidence—also known as negative data—to support its hypothesis.Congress also condemned the agency for failing to protect public health. In 2009, it issued a report, saying, “In many instances, ATSDR seems to represent a clear and present danger to the public’s health rather than a strong advocate and sound scientific body that endeavors to protect it.” The former director of ATSDR, Howard Frumkin, recognized the agency’s “need for ongoing performance evaluation and constant improvement.”ATSDR declined to respond to any particular scientist’s critiques, including the allegations of Nazario and Wargo. In an email, a representative of the agency explained that it “listened to [scientists’] concerns about Vieques” over a two-day meeting at an unspecified date. It additionally sent its 2013 report to six peer reviewers who “generally or overall” agreed with ATSDR’s conclusions and recommendations. The agency could not divulge their names, “consistent with the typical practice of peer-review journals to maintain the integrity of the peer-review process.” The agency has not redone or corrected any of its previous research.Since the government still oversees the former military base on Vieques, some scientists have resorted to deductive logic to provide possible explanations for the state of health on the island. Colón noted that neither he nor his colleagues have been able to identify an alternate source of pollution there. “The logical reasoning for all of us scientists was that if there was no other possible source of contamination in Vieques outside of the Navy’s military practices, the excess of deaths or incidence of cancer in Vieques came from the military practices,” he said.Arturo Massol Deyá, a professor of microbiology and ecology at the University of Puerto Rico at Mayagüez, has spent 17 years conducting research on Vieques—the only independent scientist to do so. Through his research, Massol Deyá has analyzed vegetation, forage samples, crabs, lagoons, and other food sources on Vieques, finding high concentrations of heavy metals throughout the island.In one of his most recent studies, Massol Deyá discovered that lead levels in manatee grass—the most abundant plant in affected areas of Vieques—were severely toxic in 2001, when the Navy began downscaling its operations on the island, but had returned to levels found in other Puerto Rican beaches by 2015. Nevertheless, he noticed a sustained increase of lead in the region’s plants, indicating the ecological impoverishment of the area.Back on the island, residents have virtually no access to health services. There is one hospital on Vieques, which has one emergency room, no pharmacy, and one birthing room with spotty air conditioning. Myrna Pagán, a cancer survivor from Vieques, said there are a handful of primary doctors on the island, but no specialists who can treat the growing number of patients undergoing dialysis. To receive chemotherapy, cancer patients have to travel to San Juan—an 80-mile trip over sea and land. The small, comparatively sparsely populated island is simply not equipped to keep up with the increased demand for specialized medical service.“Every time I go, people continue to die,” said Natasha Bannan, an associate counsel at LatinoJustice PRLDEF, formerly known as the Puerto Rican Legal Defense and Education Fund. She is part of a group that filed a petition with the Inter-American Commission on Human Rights against the U.S. government, alleging human rights abuses. “I hear stories of new people who died of cancer, of cirrhosis, of hypertension. Two of my petitioners—they’re children—were born with severe asthma,” she said.Many activists would like to hold someone accountable for the island’s health problems, but without a clear causal link to military activity, that’s proven unattainable. Bannan believes “the people of Vieques have been kept in the dark about what’s happening, and there’s no legitimate civilian input or mechanism to hold the agencies responsible.” She notes that the U.S. military is often protected under the notion of sovereign immunity, a legal doctrine that protects the government from lawsuits or other legal actions. This was why a district court and then the U.S. Court of Appeals for the First Circuit dismissed Sanchez et al. v. United States, a case filed against the U.S. in 2007 by more than 7,000 Vieques residents. The Supreme Court declined to hear the case in 2013.The mayor of Vieques, Víctor Emeric, the resident commissioner of Puerto Rico and former gubernatorial candidate, Pedro Pierluisi, the Department of Health of Puerto Rico, and the Department of Natural and Environmental Resources of Puerto Rico did not respond to multiple requests for comment on the state of public health and the clean-up process in Vieques.With legal recourse and government-sponsored research providing no clear path to action, identifying how to restore the island’s environmental health has proven more complicated. Since 2005, the U.S. Navy has managed the munitions removal and chemical clean-up process—which, they estimate, will take 10 more years on land and 15 to 20 years under water. Scientists like Nazario and Massol Deyá, along with residents, expressed concern in interviews about the Navy’s clean-up tactics—such as detonating bombs without sealed chambers and the open burning of vegetation—for their potential to exacerbate the already delicate health conditions on the island.In an email, Dan Waddill, the Navy representative who heads the Vieques clean-up process, said the Environmental Protection Agency, the Department of Defense, and governmental agencies overseas have studied the environmental and health effects of open detonations, and concluded that “open detonations can be conducted in a manner that is protective of human health and the environment.” He added that although the Navy had used closed detonation chambers in the past, the practice is “not common” and that exposure to the large, unstable munitions in Vieques could put site workers at “undue risk.”Massol Deyá thinks the clean-up can be done differently, but is more concerned about what he sees as the Navy’s lack of transparency. “Since we don’t know everything that was thrown there, the quantity, or the places, you can’t define what you should fear, what you should clean,” he said. “You don’t know what the problem is, and that’s what complicates the matter of clean-up.”While he recognizes that Vieques cannot be returned to the way it was before the Navy came to the island, he’s interested in stabilizing the island’s environment to prevent further ecological damage. “It’s a huge environmental challenge,” he said. “I believe that Vieques could be a model, but what you have here is the anti-model.” He added that mismanagement of the clean-up process has aggravated the mitigation efforts. “I’ve come to think that it’s better for [the Navy] not to do anything.”In the meantime, Vieques’s residents are trying to take care of themselves. Pagán, the cancer survivor, is now collaborating with an organization called Vidas Viequenses Valen, or “Viequense Lives Matter” in English, to address the detonations and ask research groups and federal agencies to focus attention on the island’s public-health crisis.The crisis “lies in the hands of the president,” Pagán said. Neglect at both the local and federal levels has denied people’s “dignity, their right to health, their right to happiness—and that’s not what true government should be,” she said, adding, “We need help. We are in the situation again because apparently our voices … We’re not enough people to really matter, I guess, on somebody’s scale. But, on my scale, we are very important, you know?”Bannan, the lawyer, said there’s been no redress or accountability in Vieques because the issue is largely invisible in Puerto Rico—particularly compared to the island’s financial crisis, which gets much greater attention. “People aren’t hearing bombing every day, but the health consequences are still felt,” she said. “The narrative that people in Vieques will tell you is, ‘Puerto Rico is a colony of the United States. We’re a colony of Puerto Rico.’”Yet, no matter how bad the quality of health might be on Vieques, the crisis effectively can’t be proven to the satisfaction of both government officials and scientists. Unless their approaches change, Vieques can’t be helped—leaving thousands of sick residents at an impasse.