Jones Falls Dam is a dam on the Rideau Canal located in Rideau Lakes, Leeds and Grenville United Counties, Ontario, Canada, that was built in 1831 and completed in 1832 to tame the mile-long series of rapids and falls that runs through the Jones Falls.
The dam was built by John Redpath and Thomas McKay. When completed in 1832, the Jones Falls dam was the largest dam in North America, a big accomplishment in engineering. In order to keep the water in control during construction, two sluices, artificial channels for conducting water, were kept open in the dam. The first was near the base of the dam on its east side. A second sluice was put in on the west side of the dam, about 20 feet (6 metres) above the base. To make the switch from the lower to upper sluice, the outlet of Sand Lake was blocked off. It is called the ‘Whispering Dam’ because if a person stands at one edge of the dam, near the top, and another person stands at the other edge, the two can communicate quite well over a distance of almost 360 feet (110 m). This is because of the shape of the dam in an arch and the use of sandstone rather than mortar. This abnormal quality was not planned, just a delightful result of the design.
At Jones Falls, boats rise and fall almost 60 feet via a set of four canal locks, and a dam, nicknamed the Whispering Dam, which holds back the 60 feet of water. The dam is approximately 360 feet long, 60 feet (18 m) high and 27 feet (8 m) thick at the base. It was built with large sandstone blocks that were hauled by horse-teams to and shaped on site. No mortar or cement was used in this dam. The blocks were set in a giant arch, with the pressure of the water behind the dam pushing the perfectly-dressed blocks together, like an arch used in building structures.