Marathon Lake is artificial, formed thanks to the dam. Its capacity amounts to 41 million cubic meters of water. Its maximum depth is 50 meters. The pipeline starting from the bottom of the lake transports water through the Boyati Tunnel to the Water Treatment Plants at Galatsi and then to the city of Athens. A special “water tower” was built in order to receive this water. It is equipped with water inlet ports at different levels, so as to control the depth from which water is taken depending on the time of year. For instance, in the summer, water is taken from deeper levels so that it is cooler. The high-rise water tower is also lined with Pentelic Marble. In October 1928, the water valves were installed, in order to regulate the flow in the Boyati Tunnel. Then, water was allowed to fill the lake for the first time.