Blenheim Reef (Baxio Predassa) is a submerged coral atoll in the northeastern part of the Chagos Archipelago. It measures almost eleven kilometres (North–South) by more than four kilometres (East–West), with a total area of almost thirty square kilometres, including the lagoon. The atoll has no islets or cays above the water, but is all submerged by at least four metres. The lagoon is up to eighteen metres deep. The fringing coral reef has a passage in the Southwest. The closest piece of land is Takamaka Island in the Salomon Islands Atoll, about twenty kilometres to the southwest.
