The La Jarosa reservoir (also known as the Pantano de la Jarosa or Presa de la Jarosa) is located in the La Jarosa valley, and belongs to the municipality of Guadarrama in Madrid. It is the smallest reservoir in the Sierra de Madrid, with a capacity of 7.2 million cubic metres and a surface area of 55 hectares. Despite its small size, this reservoir forms part of the catalogue of reservoirs and wetlands in the Community of Madrid. It can be accessed from the M-614 regional road.

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However, the Jarosa not only designates the reservoir itself, but also the meadows that surround its banks (making up a total area of 93 hectares), several nearby recreational areas and extensive pine forests among which the reservoir lies. In this vast area are the hermitages of Nuestra Señora de la Jarosa and the hermitage of the Altar Mayor.

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La Jarosa is included in the Guadarrama National Park. The lower area containing the reservoir would belong to the "preparque" area, considered as a regional park; the higher area of La Jarosa, adjacent to the Port of Guadarrama, is included in the National Park itself.

As well as a peaceful environment in which to relax, more activities can be undertaken in La Jarosa. The reservoir is an intensive fishing area that is periodically replenished with rainbow trout. In order to fish, it is necessary to have the corresponding licence. However, neither bathing nor other nautical activities are allowed.

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In this area you can find fish such as pike (esox lucius), black-bass (micropterus salmoides), rainbow trout (oncorhynchus mykiss) or common trout (salmo trutta).