The 147.85-kilometre (91.87 mi) river flows through the Ottadalen valley which includes the municipalities of Skjåk, Lom, Vågå, and Sel.

The watershed of the Otta drains an area of 4,172 square kilometres (1,611 sq mi) beginning in the Breheimen mountains and emptying into the large river Gudbrandsdalslågen.

[1][2] The river technically begins at the lake Djupvatnet in Stranda Municipality which is in Vestland county, about 1.5 kilometres (0.93 mi) west of the border with Skjåk Municipality in Innlandet county.

After the Vågåvatn lake at Vågåmo, it enters the Ottadalen valley and heads to the southeast to the town of Otta in Sel Municipality.

[2] The name of the river is probably derived from the Old Norse verb ótta which means to "scare" or "terrify".