| Santillana reservoir | |
| Other Name: | Manzanares del Real reservoir Embalse de Manzanares el Real |
| Pushpin Map: | Spain |
| Location: | Community of Madrid, Spain |
| Coords: | 40.055°N -3.8304°W |
| Type: | reservoir |
| Part Of: | Tagus basin |
| Inflow: | river |
| Rivers: | Manzanares river |
| Basin Countries: | Spain |
| Agency: | Canal de Isabel II Confederación Hidrográfica del Tajo |
| Designation: | Protected area (part of Parque regional de la Cuenca Alta del Manzanares) |
| Date-Built: | (renewal) |
| Engineer: | B Diaz y Diaz |
| Width: | 30km (20miles) |
| Area: | 1052ha |
| Volume: | 91hm3 |
| Elevation: | 863m (2,831feet) |
| Cities: | Manzanares el Real Soto del Real Colmenar Viejo |
Santillana reservoir, also known as Manzanares el Real reservoir (Spanish; Castilian: embalse de Santillana or embalse de Manzanares el Real), is a body of water along the Manzanares river located in the municipalities of Manzanares el Real and Soto del Real, in the Community of Madrid, in the centre of Spain. It has a maximum surface of 1052 ha, the longest distance between opposites shores reaches 30km (20miles), and the total volume of the reservoir is 91 hm³. The first dam was built in 1907, but in 1969 a new and higher dam was built. This new construction was 5 m higher, which allowed the reservoir to have a volume twice as large as before.
The second and present dam, built in a period of 12 months, began its service in 1971. Its foundations are located at an altitude of and the highest point of the dam is at 896.5m (2,941.3feet), with a total length of 1355m (4,446feet).
Belonging to the Canal de Isabel II public company, it regulates the flow of the Manzanares river and an important part of the water supply to the city of Madrid and its surroundings. Smaller rivers Samburiel and Arroyo del Mediano also flow into the reservoir, which is part of the natural protected area called Parque Regional de la Cuenca Alta del Manzanares. It is also part of the Site of Community Importance (SCI) Manzanares basin, with code ES3110004.