Railway Viaduct over the River Nidd in Knaresborough, UK

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 around 150,000 visitors a year.[citation needed] The Nidd can overflow the reservoirs, flooding the caves in the valley, in which case the river then flows along 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. The river gets its name for the Celtic word for brilliant.

The upper river valley, Nidderdale, was designated an Area of Outstanding Natural Beauty in 1994.