Alaska's largest electric utility is drawing opposition to its preliminary plans for a 700-foot-wide, 300-foot-tall concrete dam at Snow River, a salmon-spawning stream north of Seward that contributes water to the Kenai River, a world-renowned fishery.

Chugach Electric Association's plans also call for two smaller concrete dams to help the main dam store water for power generation, according to details provided by the utility to the Federal Energy Regulatory Commission in January.

One of the smaller dams would be 500 feet wide and 80 feet high, the other 300 feet wide and 60 feet high.

Bob Baldwin, president of Kenai River Watershed Foundation and Friends of Cooper Landing, groups based in nearby Cooper Landing, said he has fielded calls from people across the Kenai Peninsula and elsewhere as concerns about the proposal grow.

"We're totally opposed — forget about it (Chugach Electric)," Baldwin said he tells callers.

But the Seward Chamber of Commerce supports the idea, in part because of the economic and environmental benefits that could flow from the large, renewable energy project.

The proposed dams would create a 5,321-acre reservoir on the glacially fed river about 15 miles north of Seward, in the Chugach National Forest. At its highest, the reservoir would reach about 1,300 feet above sea level, not far from Paradise Peak, about 5 miles east of the Seward Highway.

The utility's goals include reducing its dependency on natural gas, the fuel burned to create most of its electricity, while reducing greenhouse gases, said Mike Brodie, Chugach Electric's manager of environmental engineering.

A dam could also provide a stable supply of electricity for generations of Alaskans, he said in an email statement.

The utility generally provides service to customers from the Anchorage Bowl to much of the Peninsula.

The planning process for the project is still in its early stages. The federal agency accepted the utility's application for a preliminary permit on Jan. 18, triggering a 60-day public comment period.

A preliminary permit, if one is issued, would give the utility priority over other hydroelectric projects that could potentially seek approval to build in the Snow River area, a FERC official said. The utility wants a preliminary permit for three years as it studies the project.

"This application to FERC is an initial step in a project that could take up to 10 years to complete," Brodie said.

Baldwin said the groups he represents ultimately supported the utility's effort to upgrade its Cooper Lake Hydroelectric project in the Kenai watershed near Cooper Landing, consisting of a 920-foot-wide dam in the Chugach.

The groups didn't agree with every aspect of the improvements, part of a relicensing process when the facility turned 50 years old in 2007, but the overall project was "well-done," he said.

But the groups fear this new project threatens property values and spawning areas for trout and salmon, factors that could hurt tourism, fishing and the economy in a region blessed with stunning scenery.

"No additional hydroelectric facilities are wanted on the Kenai River watershed, period," he said.

The utility said the potential impact on fish habitat is not known, but it will work with permitting agencies to address the issue. The river is listed as anadromous by the Alaska Department of Fish and Game, supporting migrating salmon such as silvers and sockeye.

"The location and extent of salmon and trout spawning habitat" is one of the main questions to be answered, said Brodie.

Also to be determined are the project's costs. The project's "economic justification" would come largely through the reduced burning of natural gas, he said.

The utility can explore a range of options under a preliminary permit, he said. But a dam and reservoir could potentially allow year-round operation, even when glacial runoff and stream-flows are reduced in colder months.

The utility has proposed two alternatives, both relying on concrete dams or concrete-faced dams containing rock-fill. Each option would generate about 75 megawatts of power, or 341 gigawatt-hours annually, according to FERC.

If a project of that size is built, it would provide 12.4 percent of Chugach's generating capacity.

Gravity would power water to rush through tunnel and a penstock, a gate or sluice — each about 14 feet in diameter — fueling three, 25-megawatt turbines in a facility east of the Seward Highway.

Under the first alternative, the tunnel and gate are longer, extending about 2 miles, roughly double the second option.

But the first alternative requires less new road construction.

Three federal agencies have filed requests to intervene in the docket, including the U.S. Forest Service and the National Oceanic and Atmospheric Administration's Fisheries Service. Friends of Cooper Landing and Kenai River Watershed Foundation are also asking to intervene.

"We are currently scheduling meetings with agencies, other interested organizations, and the public, which are expected to occur over the next couple of months," Brodie said.

Cindy Clock, executive director at the Seward Chamber, said the organization supports the project in part because it would provide renewable energy, replacing power made with heating oil or natural gas. Those fuels contribute greenhouse gas to the atmosphere.

"In August, just one-third of the fish returned for our (annual) silver salmon derby, so what is going on?" she said, suggesting changing ocean temperatures may be hurting fish populations.

The chamber also supports the possibility of reduced electricity prices the dam might one day provide, and a new source of power that increases energy security for businesses and households.

Mark Luttrell, with the Resurrection Bay Conservation Alliance in Seward, said hydropower is the dirtiest form of renewable energy, because it causes so much damage to the land.

He said he's surprised the utility has proposed a dam because of the strong opposition it will face.