In the late 1830s, the State of Ohio built Six-Mile Dam about 2.4 miles downstream of Warsaw as part of the Walhonding Canal. Contractors constructed the dam as a rock-filled, timber-crib structure with a plank facing, measuring 304 feet long and standing 4.5 feet above the river at low water. It created a slackwater pool that let canal boats cross the Walhonding River from Lock No. 4 on the south side to Lock No. 5 on the north side, where a lift lock returned boats to the canal. In 1908, the state built a new concrete dam here that ended boat traffic above the dam and converted the canal into a water supply for the mills at Roscoe Village. Engineers included three feeder gates where the new dam closed off the canal prism, using raised and lowered metal plates to regulate water flow through openings in the dam wall, and one gate operating mechanism survives. Water continued to supply the canal below Six-Mile Dam until 1978, when ODNR permanently shut the feeder gates and the channel gradually filled with silt. In 2020, the state removed the deteriorating dam with support from the Ohio EPA Division of Environmental and Financial Assistance Water Resource Restoration Sponsor Program to eliminate a safety hazard and restore aquatic habitat in the Walhonding River. River habitat improved afterward, reconnecting previously isolated endangered mussel populations and allowing native fish to return upstream to habitats where they had not been seen in more than a century.