The formation of Lake Trasimeno began in the Upper Miocene Period following high intensity orogenic movements. In the later ages, particularly during the Quaternary, other orogenic and epeirogenetic movements caused the formation of the present day basin.

Lake Trasimeno has an extensive surface area, 124 km² and is only 6.3 m deep. It is the fourth largest lake in Italy. It has a watershed area of 396 km². The shores are shallow, marshy and filled by dense submerged and emerged aquatic vegetation. It is rich in both migratory and sedentary avifauna.

There is little industry along the lake; the greater activity (in order of importance) are: agriculture (in a broad sense), fishing (in decline due to fewer fishermen) and tourism (increasing development).