The Lemme is a 35 km torrent, a right tributary of the Orba

Orba (torrente)

The Orba is a torrent of northern Italy. Its c. 70 km course runs northwards through Piedmont from its springs in the Apennines to its confluence with the Bormida, a right tributary of the Po...

, which flows through the Province of Alessandria

Province of Alessandria

The Province of Alessandria is an Italian province, with a population of some 430,000, which forms the southeastern part of the region of Piedmont. The provincial capital is the city of Alessandria....

 in northern Italy

Italy

Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

.

Its source is near Monte Calvo; from there it passes through the communes of
Fraconalto

Fraconalto

Fraconalto is a comune in the Province of Alessandria in the Italian region Piedmont, located about 110 km southeast of Turin and about 40 km southeast of Alessandria and 20 km from Genoa-Pontedecimo....

, Voltaggio, Carrosio

Carrosio

Carrosio is a comune in the Province of Alessandria in the Italian region Piedmont, located about 156 km southeast of Turin and about 45 km southeast of Alessandria. As of 31 December 2004, it had a population of 468 and an area of 7.2 km².Carrosio borders the following...

, Gavi, San Cristoforo, Francavilla Bisio

Francavilla Bisio

Francavilla Bisio is a comune in the Province of Alessandria in the Italian region Piedmont, located about 90 km southeast of Turin and about 25 km southeast of Alessandria....

, Basaluzzo

Basaluzzo

Basaluzzo is a comune in the Province of Alessandria in the Italian region Piedmont, located about 90 km southeast of Turin and about 20 km southeast of Alessandria. As of 31 December 2004, it had a population of 1,935 and an area of 15.2 km².The municipality of Basaluzzo contains...

 and finally Predosa

Predosa

Predosa is a comune in the Province of Alessandria in the Italian region Piedmont, located about 80 km southeast of Turin and about 20 km south of Alessandria....

 where it enters the Orba.

The Lemme is characterised by an extremely variable discharge

Discharge (hydrology)

In hydrology, discharge is the volume rate of water flow, including any suspended solids , dissolved chemical species and/or biologic material , which is transported through a given cross-sectional area...

; very little water flows during the summer months, but it can also give rise to significant floods, such as those of 1978.