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Lake Almanor & The Thermal Curtain

As summer heats up, the water temperatures in the lower reaches of the North Fork of the Feather River may rise above 70 degrees Fahrenheit — uncomfortably and even dangerously warm for the native rainbow trout that live there.

But cooler waters could be coming from upstream as PG&E, initially prompted by the demands of several fishing conservation groups, considers installing in Lake Almanor a contraption called a thermal curtain. This ominous-sounding arrangement is a vinyl sheet several acres in size that hangs suspended near the bottom of a lake via cables, buoys and anchors and which channels the cold water entering it straight to the outflow. The project, expected to cost $55 million, could deliver relief to trout as far as 40 miles downstream of the lake.

However, many trout fishermen and residents near the lake firmly oppose the idea and warn that taking Lake Almanor’s cold water to improve one fishery only threatens to destroy another — the trophy trout fishery of Lake Almanor itself.

The saga began in 2000, as PG&E’s 50-year license to operate three local hydroelectric projects on the Feather River — including Lake Almanor — neared its expiration date of Oct. 31, 2004. Several organizations, including CalTrout and the California Sport Fishing Protection Alliance, saw this as an opportunity to write language into the new license that would guarantee environmental improvements in the Feather River, where warm waters, conservationists say, have beleaguered the stream’s trout since the first of multiple dams was built upstream in 1914 at the southern end of what is now Lake Almanor.

In December 2000, these stakeholders settled upon a target maximum temperature of 68 degrees, and the State Water Resources Control Board (SWRCB), empowered by a provision of the Clean Water Act, mandated that PG&E devise a reliable and reasonable plan of providing such cooler waters for the Feather River. Only then could their operating license be renewed by the Federal Energy Regulatory Commission, or FERC. PG&E determined that an efficient means of providing cool water for the Feather River would be to simply draw it from Lake Almanor via a thermal curtain.

Thermal curtains exist in other reservoirs, and they may work well and without negative side effects when a lake is deep and its cold water abundant. Lake Almanor, however, is shallow — 35 to 40 feet deep over much of its area — and the thermal curtain, it has been estimated, could convey up to 50% of the lake’s trout-sustaining cold water to the Pratville Intake, the draining structure near the lake’s west shore into which most of the exiting water flows. Biologists believe such a focused removal of the lake’s cold water could have a net warming effect and cause algae blooms and oxygen depletion, and many critics warn that the lake’s abundant trophy-sized fish may even go belly up.

“Our largest concern is that this could destroy the lake’s fishery,” said Brian Morris, general manager of Plumas County’s Floodwater and Water Conservation District.

Morris says that area residents are firmly opposed to construction of a thermal curtain. “I’m not aware of any support for the thermal curtain or any other cold-water withdrawals from Lake Almanor,” he said.

In spite of opposition to the thermal-curtain plan, the SWRCB has given restoration precedence to the Feather River over Lake Almanor on the grounds that the former is a natural fishery and the latter just a manmade reser­voir, reports Dick Fording, the co-founder of the Save Lake Almanor Committee.

“But they’ve seemed to have forgotten that the Feather is a river with seven hydroelectric projects on it,” said Fording, who has collected thousands of signatures from local residents who support alternate means of pro­viding cooler waters for the trout downstream of Lake Almanor.

Chris Shutes is the FERC projects director with the California Sportfishing Protection Alliance, one of the groups that first lobbied for releasing cooler waters into the Feather River.

“We believe it’s very important to lower the river’s temperature, but we just don’t know what the best way is,” Shutes acknowledged.

In 2006, the state held its last public meeting on the matter. Subsequently, the SWRCB disappeared from the public eye to produce its draft environmental-impact report behind closed doors. That document has now been four slow years in the making. And while alternative means of cooling the waters of the Feather River were discussed at prior meetings, such as planting shade trees along the riverbank and facilitating faster movement of water downstream to reduce its time spent in the sun, until the state releases its report no serious public discus­sion of these alternatives or the thermal curtain plan can take place.

“We’re waiting for that report, and we can’t evaluate the other options until we see the other options that they’re considering,” Shutes said. PG&E, however, has discussed installing a thermal curtain multiple times in the past decade, Shutes said, “and there is reason to think that there’s going to be something to do with a thermal curtain in the board’s report.”

Victoria Whitney, the state’s deputy director for water rights, said that a draft environmental impact report can likely be expected as soon as two months from now. Whitney assured that discussion of a thermal cur­tain installation is in the report, and while 20 other alter­natives are being considered, she said, the thermal cur­tain has been regarded as “probably one of the more effective options” for reducing the Feather River’s water temperature.

Meanwhile, other opponents say a thermal-curtain system could affect not just the lake’s ecosystem but human health, as well. Fish sampled in Lake Almanor have shown trace levels of mercury, and the mud of the lake’s bottom is believed to be contaminated with the heavy metal, perhaps due in part to past gold mining activities upstream. Some locals worry that dredging the lake bottom — necessary to anchor the curtain — will unearth the buried heavy metal. Such exposure to oxygen and organic matter in the water could, they say, cause a chemical transformation called methylation that renders mercury “bioavailable” as methylmercury, the most dan­gerous form, digestible and easily absorbed into the food chain.

Wendi Durkin, president of the Lake Almanor Com­mittee, believes that installing a thermal curtain would violate the allowances of the settlement that stakeholders drafted in 2000.

“The verbiage says anything done [to lower the Feather River’s water temperature] must be within ‘rea­sonable means’,” she said. The exact wording in the fine print of FERC’s Rock Creek-Cresta Relicensing Settle­ment Agreement reads that waters in the Feather River’s North Fork should be maintained at no more than 68°F “to the extent that Licensee [PG&E] can reasonably control such temperatures.”

“We’re just not sure a thermal curtain is reasonable,” Durkin said.

Shutes notes that some critics, frustrated by the slow proceedings on the issue, have not only opposed any focused removal of Lake Almanor’s cold water but have also asked whether protecting rainbow trout in the Feather River is worth all the fuss.

“You bet it’s worth it,” Shutes said. “The Feather River’s trout are big, native trout, and they are quite spectacular.”

Indeed, many will agree that the Feather is a river worth protecting — but at what cost to the lake?


  1. David Floyd December 15, 2016

    Folks, the thermal curtain is a joke. Your talking of endangering a fishery like Lake Almanor to lower the temperature of the Feather River 1*..nonsense. I live at Lake Almanor and fish it all the time summer and winter. I see hundreds of people enjoying the lake every summer, that’s the fisherman I’m talking about, not skiers, wake boarders etc. I can also tell you that as a railroad worker I worked the Feather River Canyon for many years, 22 to be exact, in that time frame I didn’t see a hand full of people fishing the river. So, why would you want to destroy a lake that is used by many to drop a rivers temp by 1*??

  2. Lisa July 2, 2018

    Deepen Feather River…or shade it

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