Photo taken on July 19, 2018 shows people swimming in Vouliagmeni Lake in south region of Athens, Greece. Situated on an idyllic landscape, the rare geological phenomenon of the Vouliagmeni Lake attracts many visitors. (Xinhua /Lefteris Partsalis)

Photo taken on July 19, 2018 with drone shows a general view of Vouliagmeni Lake in south region of Athens, Greece. Situated on an idyllic landscape, the rare geological phenomenon of the Vouliagmeni Lake attracts many visitors. (Xinhua /Lefteris Partsalis)

Photo taken on July 19, 2018 shows people swimming in Vouliagmeni Lake in south region of Athens, Greece. Situated on an idyllic landscape, the rare geological phenomenon of the Vouliagmeni Lake attracts many visitors. (Xinhua /Lefteris Partsalis)