Electricity generated by hydroelectric plants is frequently said to be the cleanest, greenest form of power. By far the largest source of renewable energy, hydro accounts for 16 percent of global electricity generation. What's not to love? Hydro is: totally renewable, relying as it does on Earth's natural evaporation-rainfall cycle (thanks, sun!); non-polluting — no harmful emissions — and the water can subsequently be used for irrigation or human consumption; up to 90 percent efficient, compared to 50 percent for a typical coal-fired power plant; and low maintenance. Once a dam and power station are built, running costs are minimal and the facilities last for decades. Best yet, with an impoundment reservoir upstream of a power station, output can vary at the flip of a switch, since the turbines respond instantly to the quantity and "head" (pressure) of water flowing through them.

But all this goodness comes at a price, as we're seeing with the ongoing two-steps-forward-one-step-back dance to dismantle the four largest dams on the Klamath River. What's not to love — the "mean" part — is the harm dams do to fish runs. Time was, prior to 1902 when the first Klamath dam was built, Chinook and coho salmon and steelhead trout spawned in the upper reaches of the river by the million. Today, they're blocked 190 miles upstream from the mouth by Iron Gate Dam, about 20 miles northeast of Yreka. The fish hatchery at its base is scant compensation for the former glory of Klamath runs. (Fish ladders, which typically allow fish a better than 92 percent survival rate, are now routinely installed for new low dams; the height of Iron Gate, 173 feet, precludes that option.)

What about the "green" electricity generated by the powerhouses at the J.C. Boyle, CopCo 1 and 2, and Iron Gate dams? Total output for the four stations operating at full power is 163 megawatts. (For comparison, that's exactly the maximum output of PG&E's Humboldt Bay Generating Station, with its 10 new — circa 2010 — Finnish generators that normally run on natural gas.) This capacity will be lost, of course, once the dams are decommissioned. Warren Buffett's PacifiCorp, owner of the dams and power stations, is an active participant in the new dam-removal agreement, and no doubt the utility will be able to make up the loss of what is less than 2 percent of its overall output. Not incidentally, there's a lot more potential hydro capacity out there without building new dams, since less than 3 percent of the nation's 80,000 dams are used to generate electricity.

One problem with any dam, power generating or not, is sedimentation. Rivers naturally carry silt, and the faster they flow, the larger and heavier the suspended grains are. When a silt-laden river suddenly slows, as it does when entering an artificial reservoir, the silt settles out to the bottom, decreasing the storage capacity. While this isn't a huge problem in the Western U.S., where reservoirs lose about 0.5 percent of their storage capacity per year (compared to five times that in China, for instance), a century's worth of sedimentation has dumped some 20 million cubic yards of silt behind the Klamath dams.

The short-term effect on fish of releasing all that material in 2020, when the dams are scheduled to be breached, is hard to predict. Safe to say, though, the long-term effect on migrating salmon and trout will be hugely positive after having been denied their birthright for so long.

Barry Evans ([email protected]) dreams of kayaking down all 263 miles of an un-dammed Klamath.