These are the ruins of Fisher's Mill (originally the Gore Street Grist Mill, built 1834) beside Dundas Falls. Not a lot left...some stonework, an arch, some large metal artifacts pretty much buried in the soil.
Story goes that Joseph Spencer, built a mill here in 1834. Expansion happened over the years and in 1851 the Gore Paper Mill was built. Gore Mills made newsprint, carpet, felt, paper and wrapping paper. Joseph died in 1851 when he fell from the roof of one of the mills while trying to close a skylight during a thunderstorm. In 1851 the operation was sold to Robert Spence, who in turn sold them to a John Fisher in 1863.
In 1929 the mill was torn down to make room for the Dundas District school, on land donated by Robert and Frank Fisher. At that time the waterfall was also reconfigured to alleviate flooding, which gives them their man-made appearance seen today.