Water levels in the main reservoirs supplying Athens have dropped to some of their lowest points in two decades, according to new data from the National Observatory of Athens. The Mornos reservoir, which provides the majority of the capital’s drinking water, was at only 65% of its maximum surface area in May 2025, a significant decline from 79% in 2024 and nearly 100% in 2022. This marks the second-lowest level recorded since 2005.
The Evinos reservoir, which supports Mornos through an interconnecting tunnel, also showed reduced capacity, with its surface area shrinking to 2.30 km²—well below the 3.6 km² considered full. The drop in water levels is linked to consecutive years of low rainfall, reduced snowfall, and elevated temperatures, all contributing to decreased inflow and increased evaporation.
The findings come from a long-term study by the BEYOND Operational Unit of the National Observatory, using satellite data from 1984 and climate records dating back to 1950. Despite slight improvements in rainfall and snow cover in 2025, total stored water volume has continued to fall, indicating a longer-term hydrological deficit.
Athens relies on four reservoirs: Mornos, Evinos, Yliki, and Marathon. Mornos remains the primary source, while Evinos functions as a backup. The continuous decline in available water in both Mornos and Evinos highlights the growing pressure on the capital’s supply system.
Researchers note that the combined storage capacity of the two reservoirs was around 60% in May 2025. Current conditions are consistent with hydrological drought, with indicators showing reduced precipitation and thermal stress in the contributing basins. The sustained decline poses a risk to the water security of the Athens metropolitan area if dry conditions continue and no additional measures are taken.
