The Pournari dam was constructed in 1973-1976 as part of a wider effort by the Greek government to take advantage of the country’s water resources. It is the second-largest dam in Greece: its width at the top is ten meters but it widens to 450 meters at the base to be able to withstand the pressure from the 865 million cubic meters of water in the reservoir. During the dam’s construction, the Arachthos river was diverted to a 700-meter long tunnel excavated in the mountain-side next to the future artificial lake. The tunnel was sealed on 10 January 1981 and the reservoir began to fill with water.