Ohio Revised Code Title XV. Conservation of Natural Resources § 1521.09

Any landowner, or groups of landowners or lessors, in this state not within the corporate limits of any municipal corporation in this state, who shall by the construction of a dam across any watercourse form upon his own land one or more reservoirs for the collection and storage of surface water, and who maintains such reservoirs in such condition as to collect and store such water, or who donates to the state or any of its agencies a tract of land on which the state or any of its agencies may erect and maintain a reservoir for the storage of water, is entitled to a reduction of the assessed valuation of the tract of land upon which such reservoir is located of forty dollars for each acre-foot of storage capacity afforded by such dam. The total amount of such reduction shall not exceed forty per cent of the assessed valuation of the entire contiguous acreage owned by the landowner and upon which such reservoirs are located.