Fourteen thousand years ago this place lay under a mile-high ice sheet as the fourth Wisconsin glacier carved a cluster of lakes into northwest Iowa. West Okoboji is unusual among glacial lakes because of its great depth, possibly gouged by a waterfall coursing through mile-thick ice or sculpted as ice pushed glacial rubble ahead of it to form the six and a half mile-long basin later filled by melting ice as the glacier retreated. The glacial deposits here are younger by hundreds of thousands of years than those across most other Iowa landscapes, and direct contact with melting and disintegrating glacial ice created knobs, ridges, hogsbacks, eskers, kettle holes, fens, and other distinctive landforms. Nine thousand years later forests covered the area, but a changing climate and fires gave way to prairie grasses, reeds, rushes, marshlands, and fens. Beneath the waters lies a canyon of deep, dark, cool water, a lake below the lake that touches the upper waters without intermingling, while the top lake turns over twice a year because of a temperature inversion of cooling and heating. West Okoboji Lake is spring fed, has an irregular shoreline of over twenty-five miles, and is protected by wetlands whose filtering action, along with several generations of dedicated environmentalists, has helped preserve the brilliant blue water.