The Rideau Falls (French: Chutes de la rivière Rideau) are two 11-metre waterfalls where the Rideau River empties into the Ottawa River. The falls are divided by Green Island, with Ottawa’s Old City Hall just to the south.
Samuel de Champlain described the falls as “…a marvelous fall…it descends a height of twenty or twenty-five fathoms with such impetuosity that it makes an arch nearly four hundred paces broad.”
The falls were named by the early French for their resemblance to a curtain, or rideau in French. The Rideau River was later named after the falls. The Rideau Canal was constructed to bypass these falls and the Hog’s Back Falls further upstream.
Source: Wikipedia