Hayeswater is a small lake within the Lake District of Cumbria, England. The lake is situated about a mile (1.6 km) SE of the hamlet of Hartsop in the Patterdale Valley. It nestles between The Knott to its west and Gray Crag to the east and it is at an altitude of almost 1,400 feet (425 m). The lake is natural but now used as a reservoir serving the Cumbrian town of Penrith. It is fed from the south by Hayeswater Gill, which rises close to the route of the Roman High Street and continues to Cow Bridge where it joins the outlet stream from Brothers Water.