The largest stretch of inland water in central Italy and the fourth largest lake in the country, Lake Trasimene covers a surface area of 128 square kilometres with a perimeter of 54 kilometres. Of tectonic origin, the lake’s waters are fairly shallow, never deeper than six metres in normal conditions, although due to its reliance on rainfall – no rivers or streams feed the lake – water levels vary considerably from year to year as well as seasonally. These variations in the depth of the waters of Lake Trasimene, which in years with particularly high rainfalls was prone to flooding, were already a problem in Roman times when a first artificial drainage canal was built. A second canal was built with the same purpose in the 15th century by Fortebraccio da Montone, although with equally poor results. It was not until the underground drainage canal built in the mid-19th century that the problem was finally solved.
For a number of years now the lake’s water level has been low, despite receiving water from a canal built to divert flow from the river Anguillara (which is in turn fed by the Tresa, Rio Maggiore, Moiano and Maranzano). A further canal at San Savino channels the lake’s waters into the Tiber.
The lake is encircled almost completely by a natural curtain of rolling green hills, offering a soothing panorama with the highest peaks to the north standing at 800 metres above sea level. With the exception of two promontories at Castiglione del Lago and Monte del Lago, the lake’s shores run softly down to the water level. The overall shape of the lake is circular. Three islands emerge from the water at the centre of the lake: Polvese, Isola Maggiore and Isola Minore. Due to its proximity to the regional capital, Perugia, Lake Trasimene is frequently referred to as "il lago di Perugia", although to the northwest the lake borders with the Valdichiana basin of Tuscany. A total of five Comuni give onto the lake: Castiglione del Lago, Magione, Panicale, Passignano sul Trasimeno, Tuoro sul Trasimeno. All towns around Lake Trasimene are well equipped with tourist facilities as this is still a popular holiday destination during the summer months.
The natural environment
The large stretch of water that makes up Lake Trasimene supports a precious ecosystem, rich in biodiversity both of animal and plant life. Extensive colonies of juncus border the lake’s shores, which present typical freshwater marshy plant life. This is particularly luxuriant at the Oasi La Valle, which is also an important resting place for migratory birds. The surrounding hills are covered in ilex and oak forests, while the lake’s waters are rich in fish.