The "50 Hole" is a good park and play spot. The hole is under the railroad trestle right next to Rt.50. Cross over the tracks and you will see the well worn parking space and the trail to the river.
At the higher levels it tends to be a glass wave that is good for front surfing and not much else. When it gets into the lower levels it becomes more of a hole that is good for spinning and low angle cartwheels. It is an excellent place to learn to spin (my first spin was completed here).
Behind the hole there is a huge eddy, but the eddy line is tricky (sucking whirlpools, etc). Beginners might get stuck on one of these eddy lines and have trouble rolling up.
There is a slight worry about water quality, so keep your eyes and mouth shut when you flip.
Other related or nearby streams: Heritage Park to Dravo Park, Great Miami, Ohio(Class I), about 11 miles NorthEast (upstream).