Lake Wahapo (Māori: Wahapako) is a small glacial lake in South Westland on New Zealand's South Island, located within Westland Tai Poutini National Park. It sits at an elevation of 48 metres, roughly 82 kilometres southwest of Hokitika and about 16 kilometres northwest of Franz Josef / Waiau, positioned between the settlements of Whataroa and Ōkārito, approximately 7 kilometres from each. The lake measures 2.6 kilometres in length, reaches a maximum width of 1.2 kilometres, and covers a surface area of approximately 2.3 square kilometres, with a shoreline of around 6.8 kilometres.

State Highway 6 follows the southern shore for about 1.6 kilometres, making the lake straightforwardly accessible to travellers passing through the region. The lake's primary inflow is the Waitangitāhuna River, which changed course to flow into the lake in 1967, an event that considerably altered the lake's ecology. Water exits the lake via a small hydroelectric power station commissioned in 1960, discharging into the Ōkārito River.

The lake holds cultural significance as a traditional mahinga kai (food-gathering place) for local Māori. The surrounding landscape is characteristic of South Westland, with the area lying near the northern edge of Te Wahipounamu, the UNESCO-designated South West New Zealand World Heritage Area.

For paddlers interested in the broader area, the nearby Ōkārito Lagoon — accessible roughly 10 kilometres off the main highway between Lake Mapourika and Lake Wahapo — is a notable destination, described as New Zealand's largest unmodified wetland and offering guided kayak tours through tannin-stained waterways bordered by kahikatea and rimu forest. Lake Wahapo itself serves as a geographic landmark along this stretch of State Highway 6, and its easy road access from the southern shore makes it a convenient stopping point for those exploring the West Coast.