Simpson Bay Lagoon is one of the largest inland lagoons in the West Indies of the Caribbean. It is located on the island of Saint Martin. The border between the French and Dutch halves of the island runs across the centre of the lagoon. There are two small islands that lie in the lagoon: the larger, Grand Ilet to the north, is within the French region of Saint-Martin; the smaller, Little Key, to the south, is on the Dutch Sint Maarten side.