The Oglio is a left-side tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Po River

Po River

The Po |Ligurian]]: Bodincus or Bodencus) is a river that flows either or – considering the length of the Maira, a right bank tributary – eastward across northern Italy, from a spring seeping from a stony hillside at Pian del Re, a flat place at the head of the Val Po under the northwest face...

 in Lombardy

Lombardy

Lombardy is one of the 20 regions of Italy. The capital is Milan. One-sixth of Italy's population lives in Lombardy and about one fifth of Italy's GDP is produced in this region, making it the most populous and richest region in the country and one of the richest in the whole of Europe...

, 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...

. It is 280 km long.

The Oglio is formed from the confluence of two mountain streams, the Narcanello from the Presena Glacier, and the Frigidolfo, from Lake Ercavallo, in the Stelvio National Park

Stelvio National Park

Stelvio National Park is a national park in the north-east of Italy, founded in 1935.The park is the largest in Italy and covers part of two regions: Trentino-Alto Adige/Südtirol and Lombardia, in 24 municipalities....

. These two streams are born at the points of the Corno dei Tre Signori, at an altitude of about 2600 m. The streams merge near Pezzo di Ponte di Legno.

It flows in a southwest direction, through Valcamonica and then Lake Iseo

Lake Iseo

Lake Iseo or Lago d'Iseo or Sebino is the fourth largest lake in Lombardy, Italy, fed by the Oglio river.It is in the north of the country in the Val Camonica area, near the cities of Brescia and Bergamo. The lake is almost equally divided between the Provinces of Bergamo and Brescia...

. It joins the Po after traveling a zone of moraine

Moraine

A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...

 deposits, at Torredoglio, not far from Cesole and Scorzarolo, in the province of Mantua

Province of Mantua

The Province of Mantua is a province in the Lombardy region of northern Italy. Its capital is the city of Mantua.-Communes:It includes 70 comuni , ranging in area from Viadana, with 102.19 km², to Mariana Mantovana, with 8.81 km²....

. Its drainage basin

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

, which corresponds to the region of Valle Camonica, covers 6649 km². It is part of the larger Po-Adige

Adige

The Adige is a river with its source in the Alpine province of South Tyrol near the Italian border with Austria and Switzerland. At in length, it is the second longest river in Italy, after the River Po with ....

basin.