No one's calling Vermont's hydro-electric dams ugly. They hug the valleys and dot the rivers, well below ridge-top wind farms.

Who doesn't have a soft spot for a brimming, backwater lake or the misty cascades below a spillway? Who isn't transported back to the quaint, mill-spun days of early European settlement - and forward, to a low-carbon energy future?

Short answer: It's complicated. Vermont's 78 hydropower dams are popular with many ecologists - and condemned by many others. The pros and cons have supplied a bracing charge of alternating current to Vermont's green movement.

"It's hard to see people who are normally bedfellows in the environmental movement banging heads," said Jack Price, a habitat specialist with Central Vermont Trout Unlimited. Price is among those who have measured, with increasing accuracy, the long-term degradation of a watershed wrought by dams - and who simultaneously acknowledge hydropower's utilitarian virtues.

The cost-benefit debate swirling around the Green Mountain State's dams parallels (at a less catastrophic pitch) our conundrum over nuclear power. Hydropower plants generate 143 megawatts (MW) of emissions-free electricity (about 12 percent of the state's total), compared with 620 MW from the Vermont Yankee nuclear plant.

The dams' downsides are dwarfed by the nuke's, advocates say. But they are legitimate and sobering: Dams blockade rivers and take a considerable toll on fish spawning grounds.

But dams are immune from out-of-state transmission snafus, and they fine-tune Vermont's grid and rekindle it after blackouts. They also frustrate the downstream passage of nutrients and debris, critical to a wide array of wildlife. Upstream, they raise water temperatures and lower dissolved oxygen counts.

So where are we now? Decades of debate have diluted into a truce.
Dams with little potential for hydropower are slated for removal; those that generate electricity are modified to stabilize riverbanks and accommodate fish passage.

"You try for the best solution for as many people as you can," said John Voyer, Green Mountain Power's manager of power production. "You look for a rational balance."

Waterwheels and turbines have dutifully cranked out the kilowatts in Vermont since 1882.

They've kept on ticking overnight and during wind lulls. They've belched no exhaust, expelled no barrels of spent radioactive waste. They've evolved plug-and-play connectivity to the grid.

The bank of four cast-iron dynamos at the Essex Junction dam, owned by Green Mountain Power, date from 1915. In concert with the turbines at five other dams on the Winooski River, they generate the cheapest electricity in that company's portfolio.

Gary Galbraith, the plant operator, has worked at the Essex hydropower plant for 37 years. The original hardwood floors shine. The SUV-sized generators hum. To a visitor incautious enough to remove his earplugs, the engines roar.

Later, in the lunch room (a converted coal bin), Galbraith praised his workhorses.

"They have a lot of moxie and a lot of potential," he said. "They're bulletproof."

Yet there's finesse beneath the behemoths. Hefty, two-handed throw-switches and pie-plate-sized gauges, rheostats reminiscent of old Hollywood horror films - all remain on display, but their work's been taken over by winking panels of processors.

Up and down Vermont's rivers, computers and remote sensors stabilize lake levels, river flow and the pitch of every turbine blade.

Ospreys nest upstream of the Clark Falls hydropower station in Milton. The plant, installed a decade after the great flood of November 1927, houses a single, vertically mounted 3MW turbine.

Downstream on the Lamoille River, two other plants owned by Central Vermont Public Service re-use the same water molecules.

Statewide, increased flow from this year's ultra-rainy summer worked in hydropower's favor. In July, Green Mountain Power and Central Vermont reported more than twice their predicted generation levels. U.S. Department of Energy climate-change models predict more of the same in the coming century.

Will wetter forecasts float new hydro projects?

"It depends on how comfortable you are with the tradeoffs," said Kim Greenwood, a staff scientist at the nonprofit Vermont Natural Resources Council.

The appeal of cheap hydropower typically coincides with heightened public awareness about energy shortfalls, she continued. In the mid-1970s, investors rushed to renovate dam sites. This time around, she added, investors have no easy pickings: The best falls have been developed; tighter water-quality regulations stretch timelines and raise price tags.
Industry leaders in Vermont say they have no plans to build new hydro projects. But all of them plan to invest in upgrades that might squeeze an extra 10 percent out of existing facilities.

Longevity is hydro's blessing and its curse, environmentalists say.

After a long and contentious re-certification process that ended in 2005, the Peterson hydropower dam (a CVPS facility on the Lamoille that lies closest to Lake Champlain) is likely to remain operational, economical - and disruptive to generations of land-locked salmon, walleye, lake sturgeon and other fish species, said Central Vermont Trout Unlimited's Jack Price.

He and hundreds of other volunteers who challenged the utility have since shifted their efforts to other, less-costly habitat-improvement measures, such as rain gardens and streambank restoration.

Nonproductive dams, such as the one in downtown Swanton, likewise have proved resilient against the efforts of fisheries advocates to have it removed: Loyal residents claim their dam still holds historic, cultural and even sonic value.

Conversely, the Middlebury Selectboard recently made a case to the Public Service Board that aesthetics and economics should slow the addition of a turbine on the downtown Otter Creek dam.

Has political, ecological and hydrodynamic inertia reached a state of equilibrium for Vermont's dams? For now, yes."People are inherently conservative about anything that might change their landscape," Price said.

Additional Facts

What's in a megawatt?
• 1 MW: capacity, proposed Middlebury hydro plant.
• 3 MW: capacity, Clark Falls hydro plant in Milton.
• 8.5 MW: capacity, hydro plant in Essex Junction.
• 25-400 MW: estimates, undeveloped hydropower in Vermont.
• 143 MW: current, combined capacity of all Vermont hydropower.
• About 400 MW: capacity purchased from Hydro-Quebec.
• 620 MW: capacity, nuclear-powered Vermont Yankee plant.
• 1,100 MW: Vermont's peak demand (2008).

Source: Vermont Agency of Natural Resources; Vermont Department of Public Service; U.S. Department of Energy