Thorndyke Creek previously flowed under Thorndyke Road through a pair of 5-foot corrugated metal pipe (CMP) culverts. The culvert outlets were perched due to outlet scour and the Washington Department of Fish and Wildlife (WDFW) classified the site as a partial barrier to fish passage.

In 2022 Jefferson County replaced the existing culverts with a new fish-passable structure. This structure mimics the characteristics of the natural stream channel. It is 35 feet wide by 12 feet tall and the culvert bottom is filled with 6 to 8 feet of aggregate and streambed sediment to simulate a natural streambed. This has opened up access to many miles of spawning and rearing habitat for the native fish population of Summer and Fall Chum, Coho, Steelhead, and Sea Run Cutthroat.

The project was completed on October 31, 2022 for a total cost of $2,150,500, and was 95% funded by grants from the Washington State Fish Barrier Removal Board and the U.S. Fish & Wildlife National Fish Passage Program.