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.

The River Ouse is a river in North Yorkshire, England. Hydrologically, the river is a continuation of the River Ure, and the combined length of the River Ure and River Ouse makes it, at 129 miles (208 km), the sixth-longest river of the United Kingdom and the longest to flow entirely in one county. The length of the Ouse alone is about 52 miles (84 km) but the total length of the river is disputed.