The Old Hay Brook is a small river in Sheffield, South Yorkshire, England. It is formed from the Redcar Brook, Blacka Dike and another stream, which rise on moors to the south of Sheffield, and is joined by Needham's Dyke near Totley Grange. At Totley Rise it joins Totley Brook, to become the River Sheaf. Water from the river was used to power mills processing lead, corn and paper from at least the 17th century, which were later used for grinding scythes as the Sheffield metal industry expanded. All the mills were defunct by 1900, although some remnants including weirs and dams are still visible.