Well since you are posting on the Cleveland forum, I should let you know that along the Cuyahoga River there aren't really any home rental communities available. The Cuyahoga River Valley has a lot of great recreational opportunities for visitors with the Cuyahoga Valley National Park, Cleveland Metroparks, and Ohio and Erie Canalway, but not so much in terms of cottage rentals. In Northeast Ohio there are a lot of lakefront vacation communities.
To the west of Cleveland is Ohio's premier house rental and summer vacation region. It revolves around Cedar Point Amusement Park and the Lake Erie Islands. So look up places like Sandusky, Marblehead, Kelly's Island, Put-in-Bay, Bass Island, and Catawba. I'm sure you will find a lot of visitor information and home rental information.
I'm not too familar with east of Cleveland along the lakefront, but I think Geneva-on-the-Lake is a pretty popular spot for home rentals near the waterfront.
If you are still looking for "riverfront" home rentals than post on the Cincinnati forum or look to southern Ohio. I'm sure along the Ohio River there are a lot of places near Cincinnati and Marrieta.
Central Ohio and near Columbus there is an area called Hocking Hills that probably has a lot of home rentals, but I'm not familar with it.