Mazinaw Lake is a lake in the Addington Highlands north of Kaladar in Eastern Ontario. The lake is situated on the upper Mississippi River. It has a perimeter of 49 km (30 mi) and averages 41 m (135 ft) in depth with a maximum depth of 145 m (476 ft), making it the second deepest lake in Southern Ontario besides the Great Lakes. There is a narrows dividing the lake into the North Mazinaw and South Mazinaw sections.