According to Maori legend, Manapouri owes its existence to sorrow. Two sisters, Moturua and Koronae, were daughters of a chief in the region. Koronae wandered deep into the forest and became trapped after a fall. When Moturua found her sister, she realized rescue was impossible. Rather than abandon Koronae, Moturua lay down beside her, and together the sisters wept until they died. Their tears, the story goes, pooled and grew until they became the lake. It is a fitting origin for a body of water that inspires a particular kind of quiet. Lake Manapouri sits 178 meters above sea level, but its glacially carved bed drops to 267 meters below it, making it New Zealand's second-deepest lake. Thirty-three islands punctuate the surface, 22 of them forested, giving the lake a complex, multi-armed shape that looks more like a chain of interconnected waterways than a single body of water.

In the 1960s, New Zealand decided to harness Manapouri's depth for electricity. The plan required something unprecedented: a power station built entirely underground. Between 1966 and 1968, workers from the Utah Construction and Mining Company excavated straight down through 200 meters of hard rock, removing 1.4 million tonnes of stone to carve out a machine hall 111 meters long, 18 meters wide, and 39 meters high. Water from the lake drops vertically to the turbines, generates power, then flows through a 10-kilometer tailrace tunnel bored under the mountains to emerge at Deep Cove in Doubtful Sound, nine meters below sea level. The original tunnel's walls created more friction than engineers predicted, limiting output to 585 megawatts instead of the designed 700. A second tailrace tunnel, completed in 2002, brought capacity to 800 megawatts, making Manapouri New Zealand's largest hydroelectric station by output.

The power station's original design called for raising the lake level by up to 12 meters. Beaches would vanish. Islands would shrink or disappear. The lake's delicate shoreline ecology, including habitat for longfin eels whose migration the dam had already disrupted, would be permanently altered. In October 1969, Southland sheep farmer Ron McLean launched the Save Manapouri campaign. He drove across New Zealand, and within months, 14 local committees had organized. The resulting petition was the largest environmental petition in New Zealand history relative to population. The campaign became a turning point. Labour won the 1972 election promising not to raise the lake, and promptly legislated the protection. The Guardians of Lakes Manapouri, Monowai, and Te Anau were established as an independent body to monitor water levels. The Save Manapouri campaign is widely recognized as New Zealand's first successful large-scale environmental movement, a template for the conservation battles that followed.

Today, Lake Manapouri's levels fluctuate within a narrow range close to natural patterns, just as the campaigners demanded. The lake remains within Fiordland National Park and the Te Wahipounamu World Heritage Area, protected on paper and in practice. Its waters are among the clearest in Fiordland, reflecting the beech-clad mountains that surround it on three sides. The small township of Manapouri sits on the eastern shore, a settlement of roughly 270 people that serves primarily as the departure point for cruises to Doubtful Sound. From Pearl Harbour at the southern end of town, boats carry visitors across the lake to West Arm, where a coach climbs over Wilmot Pass to Deep Cove. It is one of the great day trips in New Zealand, a journey from a lake born of legend through mountains that nearly lost their shoreline to the quiet immensity of a fiord that few roads will ever reach.