New fish ladder planned for the Mill Creek Diversion Dam

The Mill Creek Channel is getting an update.

There are two fish ladders along the Mill Creek Channel: one at the Division Works - the yellow bridge near the project office - and one at the Diversion Dam, just across the river from Rooks Park.

The fish ladder at the Division Works was updated in 2020. Now, work is underway to construct a new fish ladder at the Diversion Dam.

The current fish ladder at the Diversion Dam was built in 1982 and does not meet the current criteria that define a successful fish ladder.

A fish ladder is a series of steps or slots that fish can navigate to "climb" past a dam or other structure in the river. The effectiveness of a fish ladder depends on many factors including the width of the ladder, the amount of water flow and the height of each step. These factors determine how difficult a ladder may be for fish to climb.

At the Diversion Dam, the plan is to design a fish ladder that is wider and has more steps than the current ladder. This would make the ladder easier for fish to navigate and would meet the criteria set by NOAA Fisheries standards. The current fish ladder exposes fish to turbulence and high velocities, which raises concerns for steelhead, Chinook salmon and bull trout returning to spawn in Mill Creek.

"The new fish ladder will have improved attraction flow and passage through the ladder itself, significantly reducing the amount of time fish will not be able to pass the Diversion Dam and reach spawning habitat in the upper Mill Creek." Fish Biologist Chris Peery said.

Additionally, a channel would be built next to the ladder to allow easy passage for juveniles traveling downstream. There are also plans to construct a low-flow channel to prevent fish from being trapped in the stilling basin directly in front of the dam when there is very little water in Mill Creek.

"It's a complex project and a great opportunity to partner with other agencies to improve conditions for the fish," Project Manager Karen Robison said.

The Walla Walla District is working with the Washington Department of Fish and Wildlife, NOAA Fisheries, local tribes and the Tri-state Steelheaders, to develop the new fish ladder.

The project is still in the initial design phases. The new ladder is expected to be built on the opposite side of the river from the current fish ladder. This would put it on the same side of the river as Rooks Park.

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