On my north Oregon coast rivers, logging is the main culprit. Liquidating the native forest and converting it to young tree plantations has completely changed the structure of the rivers (no more big logs and log jams), simplifying them with a host of negative results.

The hydrology has also changed. Very few people realize that these rivers used to have stable flows with little sedimentation. Now, most are very 'flashy', coming up quick and muddy; and in summer months abnormally low and warm.

Of course filling in 90+% of Tillamook Bays wetlands has reduced the juvenile rearing habitat by that much as well.