Water around and downstream from a fracking wastewater disposal facility in West Virginia contains compounds that may harm fish health by messing with endocrine systems, according to a new study.

Researchers found high levels of endocrine disruption activity in the water near or downstream from the wastewater site in Fayetteville, West Virginia. The study, published today in the journal Science of the Total Environment, adds to evidence that some chemicals in hydraulic fracturing waste are hormone-mimickers or blockers and are leaching out of wastewater disposal wells and into nearby water, potentially impacting fish and human health.

Fracking, or hydraulic fracturing, is a process that uses horizontal drilling and high volume fluid injections to release oil and gas. Along with water, the injections contain sand and a mix of chemicals—some of which have been linked to cancer, hormone impacts, and reproductive problems. It’s estimated that every well produces more than one million gallons of wastewater, which is eventually pumped into disposal wells.

There are an estimated 36,000 fracking disposal sites in the U.S. and little testing has been done on nearby surface water, said lead author Christopher Kassotis, a postdoctoral fellow at Duke University.

Kassotis and other university and federal researchers collected water upstream, downstream and around a wastewater facility that has a disposal well, holding ponds and storage tanks—all used to house excess wastewater from drilling. There is a small stream flowing through the site, which flows into Wolf Creek. Wolf Creek flows into the New River, which is used for some people’s drinking water.

Samples near the site and downstream had “considerably higher” activity for a number of hormones, including estrogen, androgen and thyroid receptors, than reference samples in the watershed far from any disposal sites.

“What’s really interesting is that they sampled from different sites that are in different places in watershed,” said Andrea Gore, a professor of pharmacology at The University of Texas at Austin who was not involved in the study. “It clearly shows substantial difference in endocrine activity looking upstream and downstream.”

The activity is worrisome for local fish—such contamination seems to affect the reproductive development of some fish species, which can lead to threatened populations. In recent years researchers are finding more “intersex” fish—male fish with some female reproductive parts—and believe the culprit is endocrine-disrupting chemicals in water.

“Sometimes we forget fish are a really important part of the ecosystem,” Gore said.

Properly functioning hormones are crucial throughout people’s entire lives, Gore said. “During development all parts of the body are going through rapid change. Most of these changes are orchestrated or at least influenced by these hormones,” Gore said. “These changes, even at really low levels, have impacts on biological development.”

And adults need normal endocrine function too, she added. “Too much or too little of any hormone, you get sick.”

Industry representatives pushed back, saying that the concentrations of compounds found do not warrant health concerns.

Endocrine-disrupting chemicals “are found in just about everything we use on a day to day basis, including dyes, perfumes, plastics, personal care products, detergents and cleaning agents,” said Seth Whitehead, a researcher at an outreach program launched by the Independent Petroleum Association of America called Energy In Depth, in an emailed response.

“Concentration level is far more relevant than merely detecting EDCs,” he added.

Susan Nagel, senior author of the study and an associate professor at the University of Missouri, said the levels found were within the range or higher than the level known to impact the health of aquatic organisms.

“In many cases, even with considerable dilution, levels of endocrine-disrupting contaminants would still be capable of disrupting the development of fish, amphibians, and other aquatic organisms,” the authors wrote.