Yliki (Υλίκη) is a natural lake in Veotia, north of Thebes, with steep banks at the foot of the western extensions of Mountain Ptoon and east of Messapia. Called also Likeri, has an average area 19.1 square kilometers. There's also an homonymous village.
In ancient times Yliki (Υλίκη) called Υλική (Material) (underlined in the ending) and took its name from the town of Ύλη (Matter), which was built on the banks of the lake as the city Akraifia. The water discharged to the nearby lake Trefia or Hungria, the younger years called Paralimni. Very close to Yliki was a great temple of the god Apollo, who had the nickname "Ptoos" by the same name of the nearby mountain.
In 1959 it began operating a water supply connection to the artificial lake of Marathon from the lake Yliki as the high population growth of Athens made most inadequate the water supply exclusively from the first. Again the increased population of Athens surpassed the capabilities of the two lakes, that since 1981 most of the water in the Greek capital's water supply comes from the artificial lake of Mornos. The drainage of the water stock in Lake Marathon is a groove and tunnel and then pumped (Mouriki-Viliza).