INDEX — The fight is intensifying over the possibility that a mini-dam for hydropower could be built on the Skykomish River.

The Snohomish County Public Utility District is studying building a small dam just above Sunset Falls near Index.

A national environmental group, American Rivers, plans Tuesday to include the south fork of the Skykomish River on its annual list of the 10 most endangered rivers in the nation.

The river will be listed at No. 7 because of the possible PUD project, said Brett Swift, regional director for the American Rivers Northwest branch in Portland.

“We recognize hydropower is important to Washington but this is no place for a dam,” she said.

Unlike the PUD’s recent small hydropower project on Youngs Creek near Sultan, the possibility of a dam at Sunset Falls has drawn opposition from several environmental organizations, along with some of the people who live near the falls.

Officials with the PUD stress they’re only studying the possibility and have not decided to build. The utility in March received a federal permit, good for three years, to examine the project.

“All we’re doing at this point is simply studying it,” PUD general manager Steve Klein said. “The opposition allows us to get input to look at everything of concern.”

Other groups, including Puget Sound Energy, have considered building dams near Sunset Falls over the years but none of the plans have panned out, according to American Whitewater, another group opposed to any dam at the site.

“This river’s kind of been under siege for decades,” said Jeff Smith, who says he lives on the river about 50 yards from where the dam would be built.

Residents’ concerns include flooding above the dam and reduced water flow below it; glare from lights; noise and traffic during construction, and the effect on the scenery.

The Sunset Falls dam would cost between $110 million and $170 million, according to the PUD’s preliminary estimates.

Water would be diverted into a pipeline above the dam and sent to a powerhouse below the falls. It would generate enough power for nearly 10,000 homes. The $29 million Youngs Creek project is expected to generate power for an average of about 2,000 homes.

While the individual dams generate only a small percentage of the PUD’s electricity, they’re part of a long-term plan to diversify power sources for the utility, officials say. This includes exploration of geothermal and tidal power and providing incentives for solar installations. The PUD currently buys 92 percent of its electricity from the federal Bonneville Power Administration.

The Skykomish is the only river in Washington or Oregon on this year’s American Rivers list, Swift said. Whether a river makes the list depends on its environmental value combined with the timing of any threats it may face, she said.

Rivers are nominated and the list is compiled anew each year, Swift said. Environmental groups and neighbors nominated the Skykomish this year, she said.

The designation carries no legal weight. It does, however, come with a call for people to let the three-member PUD board of commissioners know they’re opposed to any dam on the river, Swift said.

The river already has two listings that offer limited protection, and is up for another that could offer more.

It’s part of the state’s Scenic Rivers System. Under this designation, development is discouraged but not prohibited.

The Skykomish has been listed since 1988 as a protected river by the Northwest Power and Conservation Council, a Portland-based, power-supply planning group.

This designation also doesn’t prevent development. The Federal Energy Regulatory Commission, however, which would decide on a license for any dam, is required to consider the listing in its decision, said John Harrison, a spokesman for the agency.

The U.S. Forest Service has proposed the south fork of the Skykomish to be included on the list of National Wild and Scenic Rivers, which would prevent development. This designation has to be approved by Congress, which could take years, according to American Rivers.

The Youngs Creek project is built 1½ miles above a steep waterfall, meaning it would have no impact on spawning salmon, PUD officials said. They currently believe the same about Sunset Falls, but the coming studies will make or break the project, they say.

Other environmental groups opposing a dam on the Skykomish are the Sierra Club, American Whitewater, the state’s Hydropower Reform Coalition, the Alpine Lakes Protection Society, the North Cascades Conservation Council, The Mountaineers and Washington Wild, according to American Rivers.

Officials with the PUD said a lack of resistance was a factor in deciding to build the Youngs Creek dam. This case has attracted opposition, but to make a difference, opposition has to come from ratepayers, Klein said.

“This means the entire county in which we serve, not just a handful of people, not national organizations but people who live in the community who rely on the utility for low-cost power,” Klein said.

Bill Sheets: 425-339-3439; sheets@heraldnet.com.