like cliff said. I fish the clackamette quite often. The sandy river is a good place also. It is one of my favorites.
I dont think, in all the time Ive lived in Portland that I have ever seen people fishing where you talked about. If you walk the river by OMSI it is posted no fishing, though I have never been to the opposite side.
There is a park off of River Rd, in Milwaukie that people fish all the time. Mostly sturgeon I think.
Check this out: