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Posted 12/18/2012

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By Amber Tilton
Park Ranger, The Dalles Lock and Dam

The U.S. Army Corps of Engineers and Washington Department of Fish and Wildlife employees dewatered the east fish ladder at The Dalles Lock and Dam Dec. 3. Dewatering is done during the winter months so the fish ladders can be inspected and workers can perform needed maintenance or repairs when fish are not migrating. This is important because the ladders are the only channel for fish to get upriver and around the dam.


Workers began by lowering bulkheads, or doors, into the ladder to reduce the flow of water and lower the depth. Once the water was at a safe level, the work began.  Employees climbed down into the chilly, 30-foot wide concrete canyon and started directing fish through a maze of weirs toward the downstream exit. This slippery fish ladder is over a third of a mile long, or 1,801 feet. The weirs are staggered every 16 feet, with holes in the bottom to allow fish to swim through. Contrary to what many people think, fish usually swim through the weirs rather than jump over them.


Fish that were not guided to the downstream exit were carefully scooped into nets and placed in bags. Once contained, the precious cargo was attached to a rope and pulled out of the ladder. Up top, the staff gently took the package and lowered it over the dam and safely back into the Columbia River. Adult salmonids were released upstream of the dam and juvenile salmonids were released downstream. All other fish were released at the most convenient location except lamprey, which were held for the Nez Perce Tribe for a reintroduction program. Occasionally, a crane was needed to lift large sturgeon out of the ladders. Other fish commonly seen are steelhead, carp and shad.


After the fish were carefully returned to the river, The Dalles employees moved forward with the maintenance and repair work in the fish ladder. After the work was finished, the bulkheads were removed and the ladder was ready to again offer a safe passage around the dam.

The Dalles