The Sankarani rises in the highlands and runs north to join the Niger, the artery that gives Mali its life. At Sélingué, planners saw potential: a place where the river could be held back and put to work. The structure they built is an embankment dam with a gravity section, modest in height at just 23 meters but enormous in reach, its crest stretching 2,600 meters across the valley floor. Financed at a cost of 140 million US dollars by a coalition of backers, it came into service in 1982 and was overhauled again between 1996 and 2001. From the air, the long low ridge of the dam reads less like a wall than like a seam stitched across the landscape, holding back a body of water that did not exist a lifetime ago.

When full, Lake Sélingué holds 2.2 cubic kilometers of water and covers 409 square kilometers, its surface reaching a maximum height of around 349 meters above sea level. But it is a restless lake. The water rises and falls dramatically through the year, swelling with the rains and shrinking through the dry season, so its shoreline is never quite the same from one visit to the next. Along its irrigated edges, managed by the Office of Rural Development of Sélingué, farmers work perimeters of cultivated land that the reservoir made possible. Fishermen push out across the open water in narrow boats. The lake that displaced one way of living slowly gave rise to another.

Creating the reservoir meant relocating several villages whose land now lies beneath the surface. Researchers have returned to the area again and again over the decades since, studying what resettlement did to the families who were moved, including in surveys conducted in the late 1980s, the mid-1990s, and again between 2016 and 2018. The story they tell is the familiar, complicated arithmetic of large dams everywhere: real benefits weighed against real losses, including damage to local biodiversity and the spread of water-borne disease around the new shoreline. Behind the clean engineering figures are households who watched their fields disappear so that distant cities could keep the lights on.

Sélingué generates 44 megawatts and produces around 200 million kilowatt-hours of electricity each year, making it one of Mali's most important power sources, surpassed only by the larger Manantali Dam on the Bafing River. Its current threads out to a constellation of towns across the south and center of the country: the capital Bamako, along with Kati, Koulikoro, Ségou, Fana, Dioïla, Yanfolila, and Kalana. When evening falls over Bamako and the streetlights flicker on, part of that glow traces back to a river quietly held in check far to the southwest, doing the patient, invisible work of turning falling water into light.