Unfortunately most of the swimming spots near Portland get pretty crowded in the summer, especially on hot weekends, which is probably when most of you are planning to go out. I will try not to add to many more places that get super crowded because I know no one likes crowds. That said, punch bowl falls is one of the most popular ones, but not for no good reason. This is a great hike to a swimming hole. The trail is about 2 miles to the waterfall, and there is a nice rocky beach to set up on near the river.