The Site is composed of two islands; the larger of the two, Dyer Island, is the easternmost of a number of seabird islands off the Western Cape Province, while Geyser Island is a rocky outcrop. A sandy channel known as Shark Alley separates them. Located within the Benguela upwelling ecosystem, the surrounding seas are characterized by coastal wind-induced upwelling, which lifts cold, nutrient-rich water to the surface. As an Important Bird Area (IBA), the Site hosts around 48 bird species and it is a breeding area for 21 of them, including globally endangered seabirds such as the African penguin (Spheniscus demersus) and Cape cormorant (Phalacrocorax capensis) which number more than 35,000. The surrounding seas are inhabited by at least 11 shark species including great white shark (Carcharodon carcharias) and dusky ground shark (Carcharhinus obscurus). A further 26 fish species including the endangered galjoen have been recorded, as well as whales and dolphins. The Site also plays a role in flood control, shoreline stabilization and storm protection, and sediment and nutrient retention and export. Dyer Island Nature Reserve has a history that includes guano harvesting, egg collecting and seal harvesting. Despite strict controls and regulatory measures, there is some illegal fishing and harvesting of aquatic resources such as abalone. Recreation and tourism is limited to boat-based activities such as whale watching and shark cage diving. The Site has a management plan and a monitoring programme, which is focused on the threatened seabird species.