The Environmental Protection Agency last week finalized its long-awaited report on the impacts of hydraulic fracturing on drinking water supplies. The oil and gas extraction technique can impact drinking water resources, and the practice has affected water supplies in some parts of the U.S., the agency concluded. Six years after Congress commissioned the study, EPA says questions remain about the severity of impacts nationwide due to data gaps and uncertainties. EPA’s message on the safety of hydraulic fracturing activities is a departure from its earlier finding that the practice had no “widespread, systemic impact” on drinking water. Oil and gas industry advocates, who had found the preliminary position favorable, called the final report a political move. Environmental advocates, who began calling on EPA’s scientific reviewers more than a year ago to reconsider vague conclusions in previous drafts, lauded the changes. The revised assessment “opens the door for policy improvements and scientific advancements that could better protect the people and places most impacted,” says Mark Brownstein, vice president for the climate and energy program at the Environmental Defense Fund.