The paddle fest is an 8.5 mi. run on the Ohio River. The put in is in the Coney Island amusement park which is at the mile 72 get off of I-275. And the take out is right below the baseall satdium in downtown Cinci. For the Paddlefest barge traffic is shut down for about 6 hours but you will have to put up with them if you go it alone.
There is also put-in at a public park about 2miles north of Coney Island on route 52. That was the previous Paddlefest starting point.
And in between these places is the mouth of Little Miami River which is a designated a National Scenic & Recreational River. I have never paddle there but I have heard it's a popular paddling venue. There is a s state park on the river at Loveland which is near mile 52 of I-275