Garda Lake has a surface of 370km², while its perimeter is 162km. The maximum length of the lake basin is 51,5km by considering as reference points Riva and Peschiera, while the maximum width from Padenghe to Lazise is 17,5km. The maximum depth reaches 356m. Garda Lake has the biggest crypto-depression in the entire Italian peninsula, with its 285m under the sea level, as maximum tip. The Northern part of the lake basin is a typical sub-alpine lake basin, with an inclination angle of 5°41’.
The average surface-water temperature is 12°C, but it is subject to many variations over the seasons. In the coldest months of the year the minimum drops to 6°C, while in August the average surface temperature reaches 27°C.
The lake is characterised by an extremely slow water-exchange and the renewal cycle of 49km³ spans over 28 years. There are 83 lake tributaries, but it also receives water from subterranean veins flowing from the Adamello Mountain. The main lake tributary is Sarca, which flows into the lake at close proximity to Torbole. Among minor tributaries, Ponale, Varone and Aril can be mentioned; the latter considered the shortest Italian river.
During the last 300 years, unusual phenomena have occurred such as the frozen surface in 1709 and the flood in 1879, which reached a hydrometric height of 2,17m in Peschiera.
Among Garda Lake-phenomena, the Sesse certainly is one. It deals with a sudden rise in water level, caused by the lowering atmospheric pressure. This only happens when the lake is not choppy and it may even rise with 30cm, without any noticed event. This phenomenon generally only lasts a few minutes, while it can persist all day long on particular occasions. However, this does not influence sporty people practicing sailing or kitesurfing.
The lake currents are almost always underwater, but they can also be physically felt on the surface through the scrolling of different waters of different colours. They never have the same intensity or direction, but they may occur with more frequency in the lake in front of Bardolino, Gragnano and Garda as well as in the area between Malcesine and Limone. Where the currents develop, there’s a great temperature difference among the tributaries which flow into Garda Lake.
Garda Lake boasts the presence of some particularly beneficial thermal springs. Among the well-known there is the Boiola one, rich in Sodium and Sulphur. It flows at 300m from Sirmione peninsula at 17m depth. Since the early 19th century, this source has flowed directly into the lake giving origin to a large number of bubbles with the characteristic smell of Sulphur, which dated back to the surface. Subsequently thermal waters, which flow at 63°C with a jetsam of 245 l/s, have been channelled and taken to the lakeshore. The Boiola thermal-water is rich in trace elements, bacteriologically pure and contains a high level of Sulphur and Sodium, but also Iodine and Bromine.