We don't have access to the Lake, sorry, I didn't word my original post very well... Roehr Park is where we were and its great--a really nice, clean place... clean bathroom and all. Great for us since we have the kids... they are much happier playing on the sidewalk/grass there than in the mud or rocks on some other nasty fishing place.
In the summer months, there is a little park on the lake that is public--owned by the school district apparently (This is not the city-owned Lake Oswego Swim Park). Google "Lake Grove Swim Park, lake oswego" and you'll see it, on Lakeview Blvd. It's the only public lake access we know of, with swimming, playground, lifeguards, etc. I highly doubt fishing is allowed there, but if you live in Lake Grove or know someone who does, its free to get in and check out (come to think of it, though, I think the hours are something crazy like 12-8 daily).
If you come across any cool public places, let us know too!