Grafham Water is a reservoir with a circumference of about 10 miles (16 km). It is located between the villages of Grafham and Perry in the English county of Cambridgeshire (Huntingdonshire District). Grafham Water is the eighth largest reservoir in England by volume and the third largest by area at 1,550 acres (6.28 km⊃2;).
The lake was created by filling a valley full of water which is retained by an earth and concrete dam built by W. & C. French in 1965.
The is colonised by wildlife and a nature reserve surrounding the western side of the reservoir. The nature reserve contains semi-natural ancient (at least 400 years old) woodlands and more recent plantation woodlands, grasslands and wetland habitats such as reedbeds, willow and open water.
Grafham Water is popular for a range of leisure activities including boating, fly fishing and cycling.