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Salmon Still Under Threat Due to Mechanical Issues at Shasta Dam

A temperature control device at Shasta Dam is designed to ensure cold water is released downstream for fish, but the device doesn’t appear to work properly when lake levels are low.

Written by Alastair Bland Published on Read time Approx. 6 minutes
Disappearing salmon
Warm water released from Shasta Dam has been blamed for high rates of mortality in the Sacramento River’s winter-run Chinook salmon in 2014 and 2015.Rich Pedroncelli, AP

For well over a decade, federal officials have failed to fix a mechanical flaw in the water outflow system of Shasta Dam on the Sacramento River that fishery and river advocates say has caused millions of fertilized salmon eggs and juvenile fish to die in lethally warm river water.

This year, things are looking OK, if not good, for the Sacramento River’s winter-run Chinook salmon. The winter rains that fell over Northern California filled reservoirs, including Lake Shasta – the source of much of the cold water that spawning salmon in the river downstream depend on during and after spawning.

But in 2014 and 2015, nearly all the eggs laid and fertilized by the endangered fish were lost – partly, critics say, because a contraption known by dam operators as the “temperature control device” was leaking. This caused relatively warm water to flow out the dam during the winter-run’s spawning period, a critical time of the year when the river should be no warmer than 56F58F (13C14C). Instead, the water leaving the dam was several degrees warmer – a death sentence for developing Chinook eggs.

The TCD, as it’s often called, is a huge metal box that was bolted over the intake pipes of Shasta Dam about 20 years ago. Its front side, 300ft (90m) in height, consists of numerous shutters at different depths that can be opened and closed as needed to allow water of varying temperatures to exit the dam. The system, which cost $80 million to build and install between 1995 and 1997, came as part of an initiative to make the state’s main water supply system, the Central Valley Project, more ecologically friendly. The TCD is designed so dam operators with the U.S. Bureau of Reclamation can control the temperature of the water in the Sacramento River and, when salmon are spawning, ensure the river is cold enough.

The problem is, the device leaks around the edges. This makes it, at times, impossible for dam operators to keep water temperatures downstream of the reservoir below the lethal threshold for salmon eggs and larvae. In the extreme drought years of 2014 and 2015, for instance, the reservoir was severely depleted. There was icy-cold water deep in the lake, but the leaky TCD was unable to isolate that water into the outflow, through the dam and into the river downstream. Instead, warm water bled through the corners of the device, diluting the cold water and making it too warm. At least 95 percent, and possibly more than 98 percent, of the eggs laid and fertilized by the winter-run Chinook were cooked. The winter run, which historically saw spawning returns of several hundred thousand fish, is now at the edge of extinction.

A young Chinook salmon, called a smolt, is displayed. Sacramento River winter-run Chinook salmon numbers are critical after nearly all the fertilized eggs were wiped out by warm waters in 2014 and 2015. (Rich Pedroncelli, AP)

A young Chinook salmon, called a smolt, is displayed. Sacramento River winter-run Chinook salmon numbers are critical after nearly all the fertilized eggs were wiped out by warm waters in 2014 and 2015. (Rich Pedroncelli, AP)

Federal officials and environmentalists have known about this problematic leakage since at least 2004. It was that year that Rodney McInnis, then the regional administrator for the United States’ federal fisheries agency, told longtime water policy activist Tom Stokely in a July 23 letter, “NOAA Fisheries has become aware that the Temperature Control Device at Shasta Dam is currently not operating at optimum efficiency and needs repair.”

But in an interview with Water Deeply, Ron Milligan, the operations manager for the Central Valley Project, says the TCD is not actually supposed to be airtight to begin with. He says the whole contraption might implode against the face of the dam if water wasn’t able to leak in around the edges, which effectively relieves pressure from the outside.

“The question is, is it leaking excessively such that it’s actually defeating the purpose of having gates at different elevations?” Milligan asks.

He explains that it isn’t clear that warm water is leaking in where it shouldn’t be or that cold water is leaking through during months of the year when there is no need to release it into the river. Such circumstances would result in not enough cold water left when it is needed most by spawning fish.

Though Milligan says the device is working pretty much as designed, he also says that the device doesn’t work optimally if the lake’s level drops too low.

“This year, the device has worked wonderfully,” he says. That’s mainly because heavy rains in the winter filled the lake to higher than it’s been in years, Milligan explains. He says the device failed to work in 2014 and 2015 because it didn’t rain enough. This caused the boundary between the warm and cold water to descend lower than usual – to below the level of the big steel box’s middle gates.

“The lake was so low that we couldn’t even use the higher gates [on the TCD],” Milligan says.

All of which essentially seems to mean that the device does not work properly in all conditions – if there is a drought and Lake Shasta fails to fill up, the device cannot be relied upon to maintain suitable salmon spawning conditions.

“The TCD is obviously not working as intended because they’ve had to jerry-rig it with a tarp,” says Stokely, who serves as the salmon and water policy analyst for the Pacific Coast Federation of Fishermen’s Associations.

He’s referring to what happened after the disastrous loss of winter-run salmon in 2014. A year later, the Bureau of Reclamation, hoping to prevent a repeat of the event, draped an enormous tarpaulin over the middle portion of the device to keep warm water from leaking in. The idea was to stop or slow the leakage. But the effort came short of saving that year’s winter-run salmon. Just like the year before, nearly every winter-run Chinook egg laid and fertilized in the gravel beds between Redding and Red Bluff was destroyed in 2015.

So is there a solution that would keep water sufficiently cold for spawning salmon in the Sacramento River even during hot drought years – which are going to become more and more of a norm in the future? Possibly. Shasta Dam actually has another water intake system that leads to the river. It is located much deeper in the lake than the intake system currently being used. At this depth, it is almost always immersed in icy cold water.

However, this lower intake system bypasses the power turbines that the other intake system is connected to. Thus, using this intake – even though it can mean pure, cold water flowing over the salmon habitat below – comes with the cost of generating no electricity, which the Bureau of Reclamation sells to power providers in Redding, Roseville, Sacramento and other parts of northern California. So, the dam operators rarely use it.

But they do sometimes. Milligan says in the spring of 2015 the lower intake was briefly used as part of a strategy to conserve cold water in the lake for the fish. However, the approach failed.

Environmentalists have argued that, even in 2014 and 2015, the federal agency could have avoided the huge mortality events experienced by the winter-run Chinook – even in spite of the leaking TCD.

“We know when these fish come back, we know where they spawn, we know how much cold water they will need to spawn, and we know it gets hot in the Central Valley,” says Jon Rosenfield, a senior scientist with the Bay Institute. “The bureau has a big reservoir to store this water,” he said, but instead the agency released too much water to its customers early in the year and failed to retain enough cold water in storage.

He believes there simply isn’t a will within the agency to protect fish. Rosenfield and other environmental advocates say the agency’s top priority is delivering water to farmers even though the Central Valley Project Improvement Act and other laws make very clear that fish and ecosystem protection must be at least as high on the Bureau’s priority list.

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