A new technology could help fish stay cool as they migrate back to their spawning streams. The U.S. Army Corps of Engineers has installed “fish bubblers” near ladders at several dams on the Snake and Columbia rivers.
Fish ladders help salmon swim over or around large concrete dams. But in the summertime, they can sometimes impede salmon migration because the water inside the ladders is just too hot.
The fish bubblers will help keep the water temperatures stable for fish – and reduce heat stress that fish ladders can contribute to, said Ryan Laughery, chief of hydraulic design, dam and levee safety at the U.S. Army Corps of Engineers-Walla Walla District.
“Our job is really to provide the same environment that those fish are experiencing coming up to the dam,” Laughery said.
The bubblers mix cold water with hot surface water so that migrating fish don’t go through a roller coaster of temperatures as they travel through fish ladders upstream.
“Those bubbles have drag, and they pull that cold water up towards the surface and then mix with that warmer water at the top,” Laughery said.
They look a little something like a coiled up drip sprinkler, Laughery said. The coil sits about seven feet below the surface, where the water is much cooler. Air blown through the piping creates bubbles.
The first bubblers were installed in May at Lower Monumental Dam on the Snake River in Washington.
Cooler water, happier salmon
Salmon thrive in waters under 68 degrees Fahrenheit. Once temperatures get too hot, they will wait in cooler spots, delaying migration.
“ Historically, we have seen those temperatures in the summertime exceed that, specifically at the surface in our forebays can reach in excess of or approaching 80 degrees in those first couple feet,” Laughrey said.
Studies showed once the water temperatures in fish ladders were hotter by two-degrees, salmon started waiting it out. They’ll seek out cooler tributaries and pools until the temperatures drop. Temperatures start to get too warm around June, Laughery said, about the time sockeye salmon are migrating.
In 2015, extremely warm water and low flowing rivers contributed to harsh conditions for fish. The Snake River sockeye run that year was set to break records. Instead, most of the run died off before it reached Idaho’s Sawtooth Valley, according to the National Oceanic and Atmospheric Administration.
In addition, warmer water has less dissolved oxygen, which fish need to “breathe” underwater. The cool-water bubbles will pull oxygen up to the surface, helping improve conditions for the fish.
This isn’t the first time the corps has worked to keep temperatures in fish ladders from spiking dramatically. After a heatwave in 2015, it installed deepwater intake “chimneys” near fish ladders. Those long pipes drew up cooler water, kind of like long straws. But they proved expensive to install and maintain, Laughery said. Fish would also sometimes get stuck in the pipes.
The fish bubblers are a relatively low-cost option with much less mechanics involved.
“We just let the bubbles do their job,” he said.
A ‘cool’ innovation
As far as Laughery knows, this is a new way to use the bubblers. Previously, they’ve been used to cool aquaculture net pens, like with freshwater tilapia farms. In those instances, the bubblers helped cool the pens and bring up oxygen-rich water to the fish — similar issues the corps is trying to solve at dams in the Northwest.
While the Lower Monumental Dam on the Snake River is the first to have fish bubblers installed, it won’t be the last this summer. The corps said it also installed bubblers at McNary Dam on the Columbia River. It is in the process of installing bubblers at Ice Harbor Dam on the Columbia River and John Day Dam on the Snake River. More fish bubblers could be installed at other dams if these prove successful, Laughery said.
The older intake chimney pipes will stay in place.
The corps is conducting studies on the fish bubblers from June through September. They’re using sonar to see how the fish interact with the bubbles, said Ryan Ashcroft, a fish biologist at the U.S. Army Corps of Engineers-Walla Walla District.
“ That sonar imaging will just give us a better idea to see what kind of an impact those bubbles are having on those fish, whether there is an impact or, or not an impact,” Ashcroft said.
