Tuesday, November 17, 2015

Fish Ladder Confusion

Last week there was a front page article in The Oregonian about salmon making a big comeback.  The Bonneville Power Administration said this fall's chinook run on the Columbia River was the second-best since counting began in 1938.  A whopping 1.2 million fish returned to the Columbia and Snake Rivers to spawn.

It took many many years and many many billions of dollars to achieve this miracle, but it has finally happened.  And that is why a trip to the fish ladders at the Bonneville Dam is such an educational and inspiring trip.  Not only was I struck by the engineering of these ladders, but by their beauty.  While most people congregated on the first floor to watch the salmon from the viewing windows, I was more enthralled by the scene above--a maze of horizontal weirs that form a series of shallow steps.

As the fish enter the Columbia River, their instinct is to swim against the current to reach the spawning grounds.  When they hit the dam, fast flowing water from the end of the spillway draws them in.  The current leads them through a series of mazes that take them from one eddy-like pool to another until they get safely through.  Biologists and engineers worked together to guarantee their safe passage.  It took them awhile to get it right.  The salmon used to have to jump from one pool to the next, but now they swim underwater, in and out of vertical slots.  Not all the fish make it, of course, but 1.2 million did!


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