Experiments underway to improve salmon survival at the four lower Snake River dams include:

• U.S. Army Corps of Engineers-designed “chimneys” to pump cooler water to the surface of fish ladders. 

The top part of fish ladders, where salmon exit, are designed to accommodate the water pouring off the surface of the reservoirs, fed by gravity only. Several pumping systems add water in the bottom and middle sections to maintain water volume.

At certain times in some locations, the gravity-fed surface water can be considerably warmer than water in the rest of the ladder.

“The fish don’t like that,” said Ritchie Graves, Columbia Hydropower Branch chief for the National Oceanic and Atmospheric Administration (NOAA). “If you see a difference of about 1 degree Fahrenheit, you start seeing fish get nervous. By the time you get up to 2 degrees Fahrenheit, you see a lot of fish that are just like, ‘Nope, something’s wrong here, I’m not gonna do it,’ and they turn around and swim back down and get out of the ladder.”

The system helps make the temperature closer to the water in the rest of the ladder.

• The Corps is opening off-season surface passage routes for three hours a day, four times a week, outside the spring and summer juvenile fish spill window.

More than 90% of downstream migrating fish are choosing the surface route instead of turbines or screening facilities, Graves said.

• Higher “flex spill” levels, spilling water over spillways instead of through turbines to shorten juveniles’ travel time to the ocean.

“That’s one of the hypotheses,” Graves said. “Some people think that’s going to change things pretty substantially, other people are like, ‘Yeah, I’m not so sure.’ There could be some negative factors that counterbalance that benefit.” 

Because of the multi-year lag before the fish progeny swim back downstream, it will take years to gather enough data, he said. NOAA receives weekly updates to monitor fish health.

Keeping spillways open for five months of the year is not part of the dams’ original design, Graves said. It’s increasing wear and tear on the various hoists, bearings and mechanical systems involved.