Built on the course of the Pellegrin river at an altitude of 180 ft (55 m), the Trapan dam lake is fed by water from the watershed of this small coastal river that seems like a stream. The Pellegrin takes its source in the Maures Massif at an altitude of 590 ft (180 m) in the locality of Bormes-les-Mimosas. It flows into the Mediterranean Sea by the beach that bears its name near the Fort de Brégançon. The river marks the municipal boundary between La Londe-les-Maures and Bormes-les-Mimosas.