Environmental officials in New York have blocked natural gas drilling in the two Catskills watersheds that provide drinking water to more than 9 million people in New York City and nearby counties.

The state has not banned gas drilling in the region, but chose to leave the watersheds out of its regulatory plan for drilling in the state. The move makes it “virtually impossible” for an energy company to extract gas in the watersheds, the New York Times reports.

New York City officials strongly opposed opening the watersheds to the extraction method of hydraulic fracturing — also known as “fracking” — which shoots water and chemicals into rock in order to release gas. The practice has come under fire from environmental groups who say it can contaminate ground and surface water.

Energy companies don’t disclose the chemicals contained in their fracking fluids, saying the formulas are proprietary. But, the Pennsylvania Department of Environmental Protection supplied the River Reporter, a Narrowsburg, NY newspaper, with a list of 59 chemicals often used in fracking. They include formaldahyde, boric acid and methanol. Many chemicals on the list are carcinogens, endocrine disruptors or cause liver and respiratory problems.

Many residents of upstate New York favored drilling in the Catskills, saying it would bring a needed boost to economy, the New York Times reports.

Citing concerns that hydraulic fracturing might impact water quality “in ways that threaten human health and the environment”, the U.S. Environmental Protection Agency announced last month that it will study the impacts of fracking.

Last week, Pennsylvania officials shut down operations of a natural gas company whose leaking wells contaminated drinking water in the northeast part of the state.