Lake Marathon or the Marathon Reservoir is a water supply reservoir formed from the construction of Marathon Dam at the junction of Charadros and Varnavas Torrents near the town of Marathon, Greece. It was the primary water supply for Athens from 1931, when it became operational, until 1959. In 1959 water from Lake Yliki became available, and water from Mornos Reservoir became available in 1981.
The area of the lake at the height of the spillway of the dam is 2.45 square kilometres, the maximum depth is 54 m, the lake concentrates water from a drainage basin of 118 square kilometres with an average runoff of 14,400,000 m³ per year in an average rainfall of 580 mm per year, the average inbound volume is 12,000,000 m³ per year and the maximum reservoir capacity is 41,000,000 m³.
Address 19014, Greece
Coordinates 38°10'20.842" N 23°53'41.763" E