Lake Nipissing is a lake in the Canadian province of Ontario. It has a surface area of 873.3 km2 (337.2 sq mi), a mean elevation of 196 m (643 ft) above sea level, and is located between the Ottawa River and Georgian Bay. Excluding the Great Lakes, Lake Nipissing is the third-largest lake in Ontario. It is relatively shallow for a large lake, with an average depth of only 4.5 m (15 ft). The shallowness of the lake makes for many sandbars along the lake's irregular shoreline. The lake has many islands most of which are protected under the Protection of Significant Wetlands scheme, controlled by the Ministry of Natural Resources and Forestry.
The largest population centre on the lake's shoreline is the city of North Bay. North Bay sits along the lake's northeastern shoreline. Other notable towns include Callander (south of North Bay along Highway 11). The larger towns toward the western end of the lake are Sturgeon Falls, Garden Village, Cache Bay and Lavigne.