Balsam Lake is a lake located in the Kawartha lakes region of south central Ontario, Canada. It is 16 km long and averages 3 km wide, though its actual width varies due to the many large bays the carve its shoreline. The Gull River empties into the lake. The lake is the highest point of the Trent-Severn Waterway; from here, the waterway descends to Georgian Bay in the northwest, and to Lake Ontario in the southeast.