Lake Trasimeno

Three million years ago, there was a shallow sea in this part of Umbria. A depression formed by geologic fractures allowed the present-day Lake Trasimeno to form.

Historically, Trasimeno was known as the Lake of Perugia, being important for northwestern Umbria and for the Tuscan Chiana district. In prehistoric times, this lake extended almost to Perugia. Trasimeno is a mythological figure, joined with Agilla, a nymph born in Agello, now a hill midway between Perugia and Trasimeno, formerly an island in the lake.

The first civilization to inhabit this area was the Etruscans; three of the main Etruscan cities - Perugia, Chiusi, and Cortona - are within 20 kilometres (12 mi) of the lake. Little physical evidence remains from the period of Etruscan or later Roman settlement. Castiglione del Lago has some Roman ruins and its main streets are structured like a chessboard in the Roman style.

The Battle of Lake Trasimeno occurred on the northern shore of the lake in April 217 B.C. during the Second Punic War. The exact location of the battle is unknown because the lake then extended further north; the battle could have been fought between Cortona and Tuoro. Near Cortona is a place called 'Ossaia', in Italian meaning ossuary. Another place with reference to the battle is the place named Sanguineto, whose name is connected with the Italian term sangue meaning "blood" or, probably, "bloody place."

The Trasimeno climate is fairly warm, with moderate winters. Summers can be very warm and humid, but in general the lake moderates the climate both in cold and warm conditions because even shallow water gives a moderate thermic inertia. From May to September, the temperature is high enough to allow swimming. In 1929, a cold winter froze the whole of the lake's surface, and cars could be driven over the ice. Cold winters in 1957, 1985 and 2002 caused heavy damage to the olive trees nearby. A less severe freeze happened in 1991. Given the latitude of the lake, freezing remains a rare occurrence.

The water level of the lake is very dependent on the amount of seasonal rain and can change significantly from one year to the other. The water level is usually at its minimum level after summer (in September or October) and at its highest during spring (in April or May).

Trasimeno has high hills to the east, which help to capture rain and partially protect the lake from cold eastern winds. Most of the water in the lake comes from the network of streams on the western side of the lake. The reference water level of the lake is set at 257.33 AMSL. This level corresponds to a maximum depth of around 6m. Actions are planned to reduce the water level when it climbs above 257.60 AMSL, but since the maximum level was set the lake has reached that height only occasionally.

July 2007, a fishing boat on Lake Trasimeno

July 2008. The same boat in the same position shows how Trasimeno was suffering by water's scarcity. Since 2011, the situation has improved.

After World War II, the lake's shores retreated a kilometre in the west (the eastern shore is deeper and more steeply sloped). In 1958 the water of the lake reached the lowest recorded level, at -2.63m vs reference level. Since 1958 the level increased again to reach reference level in June 1989. After the water level started again to fall, and in 2003 the shore retreated over 100 metres (328 ft) and the level fell in October 2003 to -1.85m vs reference. From 2004 to the summer of 2006, there was plenty of rain. 150 mm (6 in) of rain fell during the last 20 days of August 2005 and over 700 mm (28 in) during the remaining part of the year. During the following five years rain was insufficient (especially in 2006 and 2007 winters were very dry and summers hot) so by October 2012 the water level was -1.51 m vs the reference. Fortunately, since 2012 the winters have been very rainy so the level of the lake has progressively increased to reach in February 2014 the reference level. In April 2014 the water level increased further to reach 0.30 m above the reference.[5]

A channel from the reservoir at Montedoglio in Tuscany to supply agriculture and lakeside towns (and thereby eliminate the need to draw water from the lake) was opened in 2012.[6]

The inhabitants of the communes around Trasimeno and the Umbrian people have successfully protected their lake, whose waters are fit for swimming and whose valleys and islands are intact environments. In 1995 a natural park was established over the entire surface and the shores. A 50 km (31 mi) bicycle path was opened in 2003 around the lake that allows tourists to explore it. There are also cross-country paths, especially over the hills on the eastern side.

The lake is inhabited by 19 species of fish, of which 15 are introduced exotics. The impact of non-native species in the lake has been heightened by the effects of climate change, which consist primarily of decreasing water levels due to lowered precipitation and increased evaporation rates, alongside reduced transparency, less dissolved oxygen and higher salinization caused by the gradual warming and shrinking of the lake. As the exotic species mostly have wider habitat preferences than the native species, the changing environmental conditions have allowed them to further establish themselves as the native fishes decline. Decline of native species is also affected by the reduction in the lake's native vegetation, such as macrophytes and the reed Phragmites australis.[7]

Commercially important native species include southern pike, tench, and European eel. The southern pike has been declining as a result of reduction in the lake's aquatic vegetation, as pikes use water plants for cover during hunting and as a substrate for laying their eggs. The increased water turbidity is also harmful to their hunting, as pikes are primarily visual predators. Efforts to counteract the southern pike's decline include a ban on its fishing, which has been in effect since 2011, and controlled restocking of juvenile specimens. Eels are also considered to be locally at risk due the presence of artificial dams and weirs impeding their ability to migrate between the lake and the Mediterranean Sea; restocking programs have been implemented in response to this.[7]

The rovella and the spined loach have historically been native to the lake, but have not been recorded in modern samplings and are considered to be locally extinct. The extinction of the rovella is linked to the introduction of non-native pumpkinseed, which competed with it for food and habitat, and to decreasing rates in dissolve oxygen in the water.[7]

Goldfish were introduced to the lake in 1988 and today make up the most common species in its fish community. Their presence has caused significant disruptions to the lake ecosystem, as their feeding on the lake bottom destroys hydrophyte coverage and stirs up sediment into the water column, increasing turbidity and causing phytoplankton blooms. They are also known to negatively impact tench populations due to competing with them for food and habitat. Other introduced species include the largemouth bass, European perch, big-scale sand smelt, topmouth gudgeon and common carp. The growing populations of goldfish, carp and gudgeon are linked to their greater tolerance for more turbid, higher-temperature water with less dissolved oxygen. Pumpkinseed has been introduced to the lake and was recorded in large numbers in 1966, but is considered to be a locally rare species in the present.[7]

The buildings are now used as social centers.

The local airport, the Eleuteri, near Castiglione del Lago, was once one of the main aviation schools in Italy, with elegant buildings that were destroyed by retreating German troops in the summer of 1944. This airport was once almost as big as Castiglione. The mild climate and perfect visibility still allow the use of this airport for air meetings.

A social center exists in the former airport. A major watercourse, the Paganico torrent, separated the airport from the town.

More than 200 aircraft come to the airshow, all light machines, because the strip is grass-covered

Before this airport was constructed, there was a hydroscale in Castiglione del Lago. On the opposite shore, in Passignano, around 10 km (6 mi) away, there was an aircraft factory, the SAI Ambrosini. This is now abandoned as an industrial center, but is still used as an association center. It was founded around 80 years ago and the buildings still exist near the Passignano sul Trasimeno railway station. This company made several types of aircraft, designed by eng. Sergio Stefanutti. Aircraft were tested at Eleuteri airport, only few kilometers away from this factory. SAI was involved mainly with Macchi during World War II. Eleuteri was also used as test center for the Ambrosini SS.4, advanced canard aircraft, which crashed in the second flight and the project was abandoned.

Trasimeno is relatively far from every major Italian city, the nearest of which is Perugia. The Foligno–Terontola railway was completed in 1866, with the main rail station in Terontola, which has been at the junction with the Florence–Rome railway since 1875. Smaller railway stations are in Passignano and Castiglione del Lago.

Because of increased traffic, about 30 years ago a highway was built over the Passignano's road to Perugia. This highway passes near the north and the east shores of Trasimeno and goes to Perugia and Assisi. Many smaller roads, such as state highway 75, are also present, especially on the western side of the lake. The Autostrada A1 passes five kilometers (3.1 mi) to the west of the Lake.

Strict regulations apply for the navigation on the Lake. A protected strip is established for the entire perimeter of Lake Trasimeno for a distance of 150 meters from the shore of the lake and the shore of the islands. In the protected strip navigation is only permitted for craft having a maximum length of 9 meters at the waterline, propelled by oars or by sail, at a maximum speed of two knots. Exceptions apply to authorised boats propelled by motor only in the water in front of port areas or authorized landing places.[8] There are ferryboats, 3 small, 2 medium, and two big (two decks) called Perusia and Agilla II, based in Passignano Port, also two dredges. There are ports in Castiglione del Lago (recently totally rebuilt), S. Arcangelo, S. Feliciano, Tuoro, and several minor anchorages.