The site is located on the south coast of the island of Unguja, commonly known as Zanzibar island, together with an associated islet. The site covers the two adjacent bays of Kiwani and Kombeni in the south-west of the island which have a soft sediment of coral silt. There is a more or less continuous stand of mangroves at the top of the bay. Chumbe island lies 5 km south-west of the mainland of Zanzibar, separated from Kombeni Bay by the Fumba peninsula. It is a small coral islet, not much more than 1 km long and only 200 m wide.
See Box for key species. The areas of silt attract large numbers of Palearctic waders and the mangroves are important roost-sites. Two tiny mushroom-coral islets a few hundred metres off the southern tip of Chumbe hold a colony of Sterna dougallii. Apart from coastal thicket species such as Nectarinia veroxii and Cossypha natalensis, Chumbe holds an interesting population of what are accepted to be Acrocephalus scirpaceus, existing in dry coral-rag thicket.
Non-bird biodiversity: None known to BirdLife International.
Pressure/threats to key biodiversity
Chumbe island is well-established as an environmentally friendly holiday resort and education centre. This philosophy requires extending to the adjacent mainland. Predation by rats and Corvus splendens is a serious problem for Sterna dougallii. The islets should be cleared of rats and Chumbe should be kept free of Corvus splendens.