The Oglio (Italian: [ˈɔʎʎo]; Latin: Ollius or Olius; Lombard: Òi, Cremonese: Ùi) is a left-side tributary of the river Po in Lombardy, Italy.

The Ogliolo stream, with an average discharge of 2.5 m3/s (88 cu ft/s) and a length of 20 kilometres (12 mi) (similar to the length of the main branch between the Frigidolfo-Narcanello merge at Ponte Di Legno and the Oglio-Ogliolo merge at Edolo) is sometimes considered as a de facto fourth branch of the Oglio river.

[citation needed] It flows in a southwest direction, through Valcamonica and enters into the Lake Iseo at Costa Volpino.

It leaves Lake Iseo at Sarnico and, after traveling a zone of moraine deposits, it joins the Po river at Torredoglio, not far from Cesole and Scorzarolo, in the province of Mantua.

The following is a list (incomplete) of the tributaries in the Camonica Valley: At Costa Volpino, the Oglio river enters the Iseo lake with a mixed delta-estuary mouth.