West Arm is a significant and historically important body of water located on the western side of Lake Manapouri within Fiordland National Park, Southland, New Zealand. It is not a river but a major arm of the lake, characterized by deep, clear water surrounded by steep, forested mountains and numerous islands. The area is most famous as the site of the Manapōuri Hydroelectric Power Station, a facility that has been central to New Zealand's environmental history. The power station discharges water through long tunnels to Doubtful Sound, and the management of lake levels here was the focus of the landmark Save Manapouri campaign. This setting provides a unique and protected environment for angling, with access primarily by boat across Lake Manapouri.