A park and play spot just a hundred yards or so downstream of the Fern Ridge dam outlet into the Long Tom River.
Park at the Army Corps Kirk Park trailhead and either put-in directly or walk 50 yards downstream until you see the obvious hole/wave created by a man-made weir structure.
It is surfable down to 700-800 cfs if you just want to practice side surfing and spins, but if you want to do loops and cartwheels, etc 1,000-1,400 is the ticket. Then above 1500 cfs it stops being retentive but can still be front surfed at 1750.
Detailed flow ranges and info is available here:
Trip Report from Wheels and Water.