The lac Otis is a body of water tributary of the southern slope of the Saguenay River via the "ruisseau aux Cailles".

A few other secondary forest roads serve the lake sector for forestry and recreational tourism activities.

The main watersheds near Lake Otis are: Lake Otis has a length of 6.2 km (3.9 mi) in the shape of a boat anchor, a maximum width of 3.3 km (2.1 mi), an altitude is 213 m (699 ft) and an area of .

The mouth of Otis Lake is located in a bay northwest of the lake, at: From the mouth of Lake Otis, the current descends the "ruisseau aux Cailles" (Aux Cailles stream) for 4.2 km (2.6 mi) to the northeast, then the northwest, to Anse aux Cailles on the shore south of the Saguenay River; then the current descends to the east the Saguenay River on 93.1 km (57.8 mi) to Tadoussac where the latter river flows into the St. Lawrence river.

The toponym "Lac Otis" was formalized on December 5, 1968, by the Commission de toponymie du Québec.