Nothing good. By the time the fish figures out it made a wrong turn in the stream, there’s not enough water to turn back, and it’s trapped—meaning certain death.
At least that’s how it used to be.
The contraption pictured above is installed on small streams to protect chinook salmon (and other fish) that swim down small stream diversions. Conservationists in the Salmon River Valleys recognize that small streams are vitally important to the remaining salmon and steelhead, but these streams are often overlooked as salmon habitat.
These little streams may not look like much at first glance, but salmon are not only a fish of large waters. After their long migration from the sea, it seems a shame for fish to be lost on the final part of their journey. Fish spawn in remarkably small streams connected to rivers like the Lemhi and Pahsimeroi:
Here’s how it works. Larger fish find an impasable metal barrier, so they turn around and swim back to the stream. But smaller fish can still pass—a fine mesh would accumulate so much debris in a day that the device would become a dam, negating its value as a diversion.
Smaller fish thus enter the pictured device and face a fine mesh barrier tube—rotated by the water wheel so that debris does not accumulate on the mesh.
The Nature Conservancy and partners consider it one of the highest conservation priorities to protect the salmon that are left. This includes a wide range of activities, including restoring habitat along spawning streams, ensuring adequate flows in rivers and devices like this one that protect both fish and agricultural practices.—Matt Miller