The Serpentine River is a river in the South West region of Western Australia.
The river rises in the Darling Scarp below Bowerling Hill and flows westward crossing Albany Highway North of North Bannister. The river continues North West through the Youarling State Forest then the Serpentine National Park. The river flows through Serpentine Dam then flows over Serpentine falls just south of Jarrahdale as it comes off the Scarp and onto the Swan Coastal Plain. The river continues West and crosses the South Western Highway then flows past the town of Serpentine. The river then veers South and continues until it discharges into the Peel Inlet near Mandurah, Western Australia.
The upper reaches of the river flow into Serpentine Dam which provides drinking water to the Perth metropolitan area.
The only tributary to Serpentine River is Big Brook. The river also flows through Kerulup Pool, Lake Amarillo and Goegrup Lake.
The river is known to have toxic algal blooms with the last occurring in 2007. Algal blooms usually occur after hot weather and in the upper reaches of the river.
Coordinates: 32°34′33″S 115°45′39″E / 32.57583°S 115.76083°E