Ohio Rev. Code § 1521.12
In the event that any dam is constructed before plans are submitted to and approved by the division of water resources as required by section 1521.10 of the Revised Code, the landowner may submit plans of the dam the landowner has built, showing the area of the drainage basin above the dam, a cross section of the dam site, a cross section, plan, and elevation of the dam, a map of the spillway, a topographic map of the reservoir basin, and such other data and information as the division requires. If the plans receive the approval of the division, and upon examination the dam is found to be satisfactorily completed in accordance with such plans, the division shall certify the completion and capacity thereof to the county auditor. If the plans fail to meet the requirements of the division, the owner may submit revised plans, and when such revised plans have been approved and the dam rebuilt to conform to such plans, the completion of the dam and its capacity shall then be certified to the auditor who shall thereupon make such reduction in the assessed valuation of the contiguous land as such owner is entitled to receive under sections 1521.09 to 1521.12 of the Revised Code.
R.C. § 1521.12