The Ōmaumau River is a middle order stream in the Auckland Region of New Zealand's North Island. It flows northwest to reach the Kaipara Harbour 20 kilometres (12 mi) northeast of Helensville. The catchment consists of rural pasture and fragmented native forest.

• List of rivers of New Zealand

• "Place name detail: Ōmaumau River". New Zealand Gazetteer. New Zealand Geographic Board. Retrieved 12 July 2009.
• Omaumau River - Land Air Water Aotearoa (LAWA)