A Volcanic Reservoir
Lake Bracciano, located 32 kilometers northwest of Rome, occupies a depression formed by the collapse of a magma chamber. This volcano-tectonic activity, part of the Sabatini volcanic complex, occurred between 600,000 and 40,000 years ago. The lake is the second largest in the Lazio region, with a surface area of 56.76 square kilometers and a maximum depth of 165 meters. It is fed primarily by rainfall and underground springs, with a single outflow, the Arrone river. Since 1986, the lake has been a protected drinking water reservoir for Rome, which strictly forbids the use of motorboats on its surface.
The lake’s connection to Rome is ancient. In 109 AD, Emperor Trajan inaugurated the Aqua Traiana, an aqueduct that channeled water from springs near the lake to the city. This structure supplied water for grand projects like the Baths of Trajan and a large basin for mock naval battles. The aqueduct was cut during the Gothic Siege of Rome in 537 AD but was repaired. In the early 17th century, Pope Paul V commissioned its reconstruction to alleviate water shortages, renaming it the Acqua Paola.
The 2017 Water Crisis
In 2017, a combination of low rainfall and high water extraction led to a severe drop in Lake Bracciano's water level. Below-average precipitation since 2015, which was 50% lower than the 1961-1990 baseline in 2017, was a contributing factor. Intense summer evaporation, reaching 6.7 mm per day, further stressed the lake. The primary driver of the crisis, however, was water withdrawal by Rome's utility company, ACEA, to compensate for the city's drought and leaky pipe infrastructure.
Satellite monitoring showed a drop of approximately 1.6 meters between May 2016 and November 2017. By November 2017, the lake reached a historic low, falling 198 centimeters below the hydrometric zero (the reference water level). This drop far exceeded the maximum sustainable limit of -150 cm, a level established to protect the lake's ecosystem. The receding waters exposed large areas of the lakebed, increasing the beach by 10-15 meters in some areas. This had severe ecological consequences, causing the desiccation and death of shoreline and underwater vegetation, which serve as important fish habitat. The crisis also affected bird nesting sites and led to an increase in phosphorus concentrations due to the reduced water volume, threatening the lake's self-purification capacity. In response, the Lazio Region issued an ordinance on July 20, 2017, forcing a halt to water pumping by ACEA to preserve what remained of the lake's ecosystem.