The Great Sheffield Flood was a flood that devastated parts of Sheffield, England, on 11 March 1864, when the Dale Dyke Dam broke. The newly-built dam, at Low Bradfield on the River Loxley, broke while it was being filled for the first time. An estimated 3 million m3 (700 million imperial gallons) of water swept down the Loxley Valley, through Loxley village and on to Malin Bridge and Hillsborough, where the River Loxley joins the River Don. The flood continued south down the Don into Sheffield centre, around the eastward bend of the Don at Lady's Bridge, then to Attercliffe, past the sites of today's Don Valley Stadium, Sheffield Arena and Meadowhall Shopping Centre and on to Rotherham. The subsequent enquiry found that the flood had wrecked nearly every bridge as far as Lady’s Bridge, destroyed 800 houses, and killed 270 people - bodies were later found as far down the Don as Mexborough. The conclusion was that the dam construction was defective, and that a small leak in the wall grew rapidly until the dam failed completely.
The claims for damages formed one of the largest insurance claims of the Victorian period.