Lake Nipissing (; ) is a lake in the Canadian province of Ontario. It has a surface area of , a mean elevation of above sea level, and is located between the Ottawa River and Georgian Bay. Lake Nipissing is the third-largest lake entirely in Ontario. It is relatively shallow for a large lake, with an average depth of only . The shallowness of the lake makes for many sandbars along the lake's irregular shoreline. The lake reaches a maximum depth of 64 m (210 ft) near the mouth of the French River, off the shore of Blueberry Island. 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.