The lake occupies an unfilled lobe of a former glacial trough and is enclosed by moraine walls to the north, south and west.

[11] Wahapako was a traditional mahinga kai (food-gathering place) for local Māori, who would come to the lake to gather longfin eels.

The scheme was built at a cost of £40,000 to provide reliable electricity supply to about 90 customers in the Whataroa area, and included 47 kilometres (29 mi) of 11,000-volt transmission lines.

The local territorial authority at the time, the Westland County Council, levied a special rate to fund the project.

In 1990, the scheme was redeveloped, resulting in an increased maximum generation capacity of 3.1 MW, and an average annual output of 15.3 GWh.

The river's new course after the avulsion was across an ancient alluvial fan and through a stand of kahikatea (Dacrycarpus dacrydioides) at the northeastern end of the lake.

Silt was quickly deposited in the kahikatea forest, burying the low understory vegetation and causing widespread mortality of the trees at the head of the lake.

[10] Tōtara (Podocarpus totara), miro (Prumnopitys ferruginea), mountain horopito (Pseudowintera colorata), patē (Schefflera digitata), and mikimiki (Coprosma rotundifolia) also survived by producing adventitious roots.

[21] Since 1967, the silt-laden water of the Waitangitāhuna River has caused an increase in the turbidity of Lake Wahapo, and a concomitant reduction in light penetration.