Lac Salé is a crater lake of seawater on the north coast of Grande Comore, the main island of the Comoros in the Mozambique Channel, a few metres above the sea in the mouth of an old volcanic vent, its colour shifting from jade to turquoise by the hour, and it is circled on foot along a lava ridge with the Indian Ocean on the other side. The lake is one of the dozens of small mouths of La Grille, the volcano that makes the north of the island, and the sea seeps into it through the porous lava, so it rises and falls with the tide and is saltier than the ocean; Comorian tradition says a village stood in the hollow until a barefoot stranger came asking for water and every household turned him away but one old woman's, after which the ground opened and drowned the rest, and the lake is treated with caution, swum in by few. A rough footpath runs right around the lip of the crater, the salt lake on one side and the open ocean on the other, with the white beaches of Maloudja and Mitsamiouli ten minutes below, where the coconut palms all lean seaward, bent one way by the trade winds, over a fringing reef that is clear in the dry season.
The bay west of the lake is the Trou du Prophète, the Prophet's Hole, where the Prophet is said to have sheltered a boat. From July to October humpbacks come up from Antarctic waters to calve in the warm channel, and the boats run out from the north coast, cut the engine and wait for the mothers and calves to pass; from November to April the northwest monsoon the Comorians call kashkazi throws sudden walls of rain across the coast, bright morning to grey downpour in minutes, then a hard clean light afterwards. Lac Salé is a piece of the sea trapped in a volcano, and the story of the village under it keeps the swimmers out.