A new report from the Environmental Protection Agency suggests that hydraulic fracturing does have the potential to affect drinking water resources in the U.S. The report represents a shift in the agency’s previous conclusions, published in a draft report in 2015, which suggested low impacts from fracking.

The final report, released Tuesday, relies on a review of more than 1,200 previously cited scientific sources, as well as new research conducted for the report and an independent peer review by the EPA’s science advisory board. The report finds a range of possible impacts, from temporary changes in water quality to the complete contamination of drinking water wells.

Drinking water can be affected at any stage of the fracking process, the report notes, from acquiring the water that will be used to injecting it into production wells and disposing of the wastewater afterward. Impacts are generally seen at sites close to production wells.

“The value of high-quality science has never been more important in helping to guide decisions around our nation’s fragile water resources,” said Thomas Burke of the EPA’s Office of Research and Development.

In 2015, a draft report found that fracking has caused isolated instances in which drinking water was affected, but did not bring about “widespread, systemic impacts” on drinking water. Environmental groups criticized the draft.

The final report includes a slightly stronger set of conclusions. It claims that fracking activities “can impact drinking water resources under some circumstances,” and notes that certain activities or conditions may make these impacts more severe. However, the report also notes that significant data gaps and uncertainties in the data prevent a detailed assessment of how often any given activity harms water quality or how serious the effects are on a broad scale.