Can access river from MS Young Park. Use the upper lot and hike to the bottom of the trails. Multiple ways to get down to the river. You can also park at the end of Mapleton and hike in. Once you are at the river, look for an outcropping of rock(s) about in the middle of the park's waterfront. That is a very good small mouth area. Bring a plastic bag and pack out some of the trash from those that leave trash behind. Gets a bit ugly at that location.
From that location, can go north along the bank and eventually bump in to the ramp that will get you on Cedar Island. Fish the inside cove, most popular is the south end of the cove. The floating logs at the NW end have crappie but you need a float tube or the like. Carp, smallies are along the banks inside the cove.
There are also fishing docks WL side below Willamette Falls.
When you are fishing these areas, ask others where they fish along the river.
Also know any where along the river bank below the ordinary high water mark is considered Public Greenway. Most of the property owners along the river are cool with it. If you run in to one not, just move on.