The northern part of the lake is narrower, surrounded by mountains, the majority of which belong to the Gruppo del Baldo. The phallic shape is typical of a moraine valley, probably having been formed under the action of a Paleolithic glacier. Although traces of the glacier's actions are evident today, in more recent years it has been hypothesised that the glacier occupied a previously existing depression, created by stream erosion 5 to 6 million years ago.
The lake has numerous small islands and five main ones, the largest being Isola del Garda. Nearby to the south is Isola San Biagio, also known as the Isola dei Conigli ("Island of the Rabbits"). Both are offshore of San Felice del Benaco, on the west side. The three other main islands are Isola dell'Olivo, Isola di Sogno, and Isola di Trimelone, all farther north near the east side. The main tributary is the Sarca River, while the only outlet is the Mincio River.
If the water level of the Adige river is too high, excess water is diverted to the lake through the Mori-Torbole tunnel.