Trout Lake is a lake in municipalities of East Ferris and North Bay, Nipissing District in Northeastern Ontario, Canada, approximately 6 kilometres (4 mi) east of the much larger Lake Nipissing. Trout Lake is the source of the Mattawa River and a significant body of water on a well-known historic North American voyageur (fur-trading) route. It is about 11 kilometres (7 mi) long and 4 kilometres (2 mi) wide and exits eastward into the Mattawa River, which flows via the Ottawa River to the St. Lawrence River.