In the late 1830s, the State of Ohio built the Six-Mile Dam about 2.4 miles downstream of Warsaw as part of the Walhonding Canal. Contractors constructed it as a rock-filled, timber-crib dam with a plank facing, 304 feet long and 4.5 feet above the river at low water. The dam 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 replaced it with a concrete dam that ended boat traffic above the dam and turned the canal into a water supply source for the mills at Roscoe Village. Engineers included three feeder gates to control water flow by raising and lowering metal plates over openings in the dam wall, and the canal below Six-Mile Dam continued to receive water until 1978, when ODNR permanently closed the 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 address a safety hazard and restore aquatic habitat in the Walhonding River, improving habitat quality, reconnecting previously isolated endangered mussel populations, and allowing native fish to return upstream to places where they had not been seen in over a century.