An outer reef is a type of coral reef that forms at some distance from the shore, usually in deeper water. It typically consists of a rim of shallow-water corals around a lagoon or seaward side of an island or coastline. Outer reefs are often found in areas with strong currents and high wave energy, which can help to maintain their health by providing nutrient-rich waters and preventing the growth of competitive algae on the coral colonies. These reefs provide important habitats for a wide range of marine life, including fish, invertebrates, and other organisms that rely on coral ecosystems for their survival.