A conservation group listed the Hoback River as one of most endangered rivers in the United States, saying it faces the threat of pollution from a proposed gas field in the Noble Basin area of the Wyoming Range.

The group, American Rivers, ranked the Hoback seventh in its 2011 America’s Most Endangered Rivers list, released today.

“Listing the Hoback this year was a no-brainer,” said American Rivers northern Rockies director Scott Bosse. “It’s one of the most pristine rivers in the country, and it faces an immense threat from oil and gas drilling.”

Congress designated the lower Hoback as a Wild and Scenic River in March 2009 as part of the Snake River Headwaters Legacy Act.

“I can’t think of another case in the United States where industrial-scale gas drilling has been proposed at the headwaters of a Wild and Scenic River,” Bosse said.

In particular, officials at American Rivers worry about the impacts of a proposal by Plains Exploration and Production Company to drill 136 gas wells immediately south of the river. Runoff, a spill or contamination of the aquifer could channel pollution from the gas field directly into the Hoback River’s headwaters, Bosse said.

“We think there is clear and present danger to groundwater resources and surface water resources,” he said. “We think that the Forest Service hasn’t fully considered what a worst-case scenario would look like at the Hoback headwaters.”

Opponents of the gas field in Noble Basin were pleased with the endangered listing for the Hoback.

“This is certainly consistent with our concerns regarding water issues on the upper Hoback,” said Dan Smitherman, spokesman for Citizens for the Wyoming Range. “At the top of the list would be some type of spill or some type of discharge directly into the river. And we don’t know what kind of interconnectivity there is between the aquifer and the streams that feed the river.”

Smitherman said the issue is bigger than the lower Hoback’s Wild and Scenic designation.

“It’s more fundamental than that,” he said. “It’s an important fishery, and any type of pollution at all could be devastating to that ecosystem.”

The news comes on the heels of a Duke University study that found high levels of methane in drinking water near gas well sites in New York and Pennsylvania.

Plains Exploration and Production Company was responsible for a recent spill in California that dumped 40 gallons of crude oil and 400 gallons of brine water into a Rio Hondo River tributary.

Plains officials dismissed the endangered listing, saying they have taken pains to make sure water resources are protected.

“The American Rivers organization has consistently opposed all forms of oil and gas development in the region, and this announcement is essentially a reiteration of that policy statement,” Scott Winters, vice president of corporate planning and communications for Plains Exploration and Production Company, said in an email. “PXP has not been contacted by American Rivers to discuss our proposed project or to offer a buy out of the leases.

“PXP is sensitive to community concerns about protection of ground and surface water quality in the area surrounding the project,” Winters continued. “PXP has taken extra steps as part of the Wyoming Range Conservation Agreement to design as many protections as possible for water resources in the area. Among other things, PXP has agreed to relocate two pad locations to create an additional buffer between the Hoback River and some of the drilling operations.”

The Bridger-Teton’s environmental review of the project will tell whether or not the wells would truly impact the Hoback River, Winters said.