Boisseau islet is a massive 1.2-acre (0.54 ha) complex rising to 82 ft (25 m) above sea level. It is formed by an andesite flow circumscribed on all sides by sharp, moderately high but very steep and fragile cliffs that offer few possibilities of docking and are subject to breaking waves in their eastern part, not protected by reefs. It is one of the furthest islets of Baie du Robert at the outer limit of the haven it represents and 1,640 ft (500 m) northeast of Madame islet. Uninhabited and devoid of any construction, Boisseau islet is a recognized and protected sanctuary for birds. Roseate terns, bridled terns, ruddy-breasted seedeaters, and square-tailed doves are found in abundance there.