Structures to help salmon passage will be constructed in a section of the Mill Creek flood-control channel shown here between Park and Otis streets in Walla Walla. Funds for this project are among several the the state Salmon Recovery Board recently awarded to local fish recovery organizations.

WALLA WALLA — Washington state is giving the Tri-State Steelheaders $4.7 million to continue fish passage work in Mill Creek in Walla Walla, the organization recently announced in a news release.

The grant comes from the Recreation and Conservation Office, and will fund work at four sites, including at Roosevelt Street, between Spokane and Park streets, between Third and Sixth avenues and in the channel above Roosevelt Street, according to the release.

Tri-State Steelheaders Executive Director Brian Burns said much of the work will be done on the smooth concrete that allows water to pass at speeds fish can’t handle.

The organization has been working on Mill Creek in Walla Walla since 2011.

The flood control portion of the creek includes two miles of concrete-lined channel that is good for flood control, but bad for fish passage.

“The short description of what we do is we cut and remove a strip of the smooth concrete from one side of the trench,” he said. “The problem is that all the concrete there is smooth. It doesn’t slowdown (water) anywhere. So, we’re replacing it with some concrete that has basically blocks or roughness that creates friction with the water. That slows the water down to a velocity that the fish can swim without becoming exhausted.”

The goal is to slow the flow of the water in certain areas of the creek, but not in the whole creek.

“What happens if you slow water down is it piles up,” he said. “This is a flood control channel. One of our design criteria is we do not increase the flood elevation in the channel with our projects.”

The project is coordinated with Walla Walla County Public Works Department, which helps ensure that plans for the project will not hurt flood prevention efforts.

Further, the Tri-State Steelheaders need licenses for each project from the Army Corps of Engineers, which also ensures the projects will not harm flood control efforts.

The work between Third and Sixth avenues will coincide with the city’s plan to remove bridges on Fifth and Sixth avenues. The support piers that current bridges have in the channel take up too much room to have the fish passage. The scope of the work that involves the $4.7 million is expected to be complete by 2025.

“Part of our design requirements is that we have to leave room for the Public Works department to get their maintenance vehicles up and down both sides of the channel,” Burns said.

Burns said new bridges to replace the removed ones would be designed differently and not have the support pier in the channel.

Improving fish passage in Mill Creek, according to the release, is part of the organization’s greater efforts to restore sustainable populations of native fish.