Rogue River salmon and steelhead will begin migrating over the Savage Rapids Dam fish ladder late Monday for one final run as construction crews prepare to remove the 88-year-old dam.

Rogue River salmon and steelhead will begin migrating over the Savage Rapids Dam fish ladder late Monday for one final run as construction crews prepare to remove the 88-year-old dam.

The two primary coffer dams essential for removing the dam will be finished by Monday, one day ahead of its three-week window for completion, said Bob Hamilton, the Bureau of Reclamation's project manager.

The temporary coffer dams will allow Slayden Construction Group crews to close the radial gates and raise the water surface behind the old dam. That will return water flows to the fish ladder, which has been dry since April 7.

The coffer dams will keep water away from half of the existing dam's walls, creating the dry working environment construction crews need to begin demolishing the dam's north side.

Once that's completed, crews plan to remove the coffer dams and divert the river through the breached section of the dam, which is expected to occur by October.

Removal of two additional chunks of the dam's south end were scheduled to be done by mid-December, ending the $39.3 million effort to rid the Rogue of its single biggest fish-killer.

The dam will be replaced by an already completed electric pumping station, which is ready to begin water delivery for the Grants Pass Irrigation District when its irrigation season begins in mid-May.

The coffer dams were completed under a permit issued by the Oregon Department of Fish and Wildlife, whose biologists were concerned that high flows could impede fish passage at the facility.

The work was done during the tail-end of the Rogue's winter steelhead run and the beginning of its spring chinook run upstream toward upper Rogue spawning grounds.

Dan VanDyke, the ODFW's Rogue District fish biologist, said a lack of rain has kept Rogue flows low enough to keep fish from wallowing downstream of the dam.

"The weather's been absolutely perfect," VanDyke says.

Biologists have estimated that it takes spring chinook seven to 10 days to migrate the 19 miles between Savage Rapids Dam and Gold Ray Dam's video fish-counting station, VanDyke says.

Counts at Gold Ray Dam reveal that 179 spring chinook and 305 winter steelhead passed there between April 17 and April 20.

"Based on that, I'd say at least some of the fish are passing through the radial gates," VanDyke says.

Reach reporter Mark Freeman at 776-4470, or e-mail mfreeman@mailtribune.com.