Knaresborough Castle is a ruined fortress overlooking the River Nidd in the town of Knaresborough, North Yorkshire, England.

The River Nidd is a tributary of the River Ouse in the English county of North Yorkshire. In its first few miles it is dammed three times to create Angram Reservoir, Scar House Reservoir and Gouthwaite Reservoir, which attract a total of around 150,000 visitors a year. The Nidd can overflow the reservoirs, flooding the caves in the valley. In such cases the river overflows into the normally dry river bed past Lofthouse through to Gouthwaite Reservoir. The Yorkshire Dales Rivers Trust YDRT has a remit to conserve the ecological condition of the River Nidd from its headwaters to the Humber estuary.