The Nanaimo River Watershed area contains Cedar, Duke Point, Extension, South Wellington, and portions of Regional District of Nanaimo Electoral Areas A and C (see map below).  The Nanaimo River originates from Mount Hooper and flows 78 km to its mouth at the Nanaimo River Estuary, which is located at the south end of the Nanaimo Harbour. Over its course the Nanaimo River and its tributaries drain an area of approximately 813 km2. The major tributaries of the Nanaimo River are North Nanaimo River, South Nanaimo River, and Haslam Creek. The watershed includes two natural lakes (First and Second Nanaimo Lakes) and 3 man made lakes. 

The 2 natural lakes are both located on the North Nanaimo River.  Three man made structures, including the Jump Creek Dam, the South Fork Dam, and the Fourth Lake Dam, create the three large man made lakes.  Jump Creek and South Fork dams are on the South Nanaimo River.  The City of Nanaimo operates these two dams to supply water to the Snuneymuxw First Nation, the City of Nanaimo’s residents, and the South West Extension Improvement District. The Fourth Lake Dam and reservoir is located on Sadie Creek in the upper reaches of the North Nanaimo River catchment, and is operated by Harmac Pacific (Harmac).

The upper watershed is mainly unpopulated forestry land. The southern portion of the watershed is primarily rural with areas of agriculture, urbanization and industrial activity.