The Great Sheffield Flood was a flood that devastated parts of Sheffield, England, on 11 March 1864, when the Dale Dyke Dam broke as its reservoir was being filled for the first time. At least 240 people died and more than 600 houses were damaged or destroyed by the flood. The immediate cause was a crack in the embankment, the cause of which was never determined. The dam's failure led to reforms in engineering practice, setting standards on specifics that needed to be met when constructing such large-scale structures. The dam was rebuilt in 1875.

Sheffield is a city in South Yorkshire, England, whose name derives from the River Sheaf which runs through it. The city serves as the administrative centre of the City of Sheffield. It is historically part of the West Riding of Yorkshire and some of its southern suburbs were transferred from Derbyshire to the city council. It is the largest settlement in South Yorkshire.