There is similar work going on to restore fish passage underneath I-90 near Issaquah, Washington. Although in that case, the part of the streams that's currently inaccessible is less than a mile for most of them, and 2 miles for one of them. It's a major undertaking to restore a stream bed or channel underneath the interstate.

This will benefit Kokanee Salmon, a kind of salmon that spends all its life in fresh water and does not migrate to salt water like most salmon.

In Lewis Creek, they currently have access to only 1/2 mile of the creek, but in 2021 there were about 1000 of them returning (from Lake Sammamish) to spawn.

That's really surprising that they could survive with such a small range! How are they counted during their migration?