The park includes a complex eco-system with outstanding landscapes. The five inter-linked ecosystems in the park are: a marine system characterised by the warm Indian Ocean, containing the southernmost coral reefs in Africa, as well as sub-marine canyons and long sandy beaches; a coastal dune system consisting of high linear dunes and sub-tropical forests, grassy plains and wetlands; lake systems including two estuary-linked lakes of St Lucia and Kosi, plus the four large freshwater lakes of Sibaya, Ngobezeleni, Bhangazi north and Bhangazi south; the Mkhuze and Umfolozi swamps, with swamp forests and extensive reeds and papyrus marshes; an inland system which includes ancient shoreline terraces and dry savannah woodlands.
A substantial game reintroduction program is in progress bringing in black rhino, buffalo, waterbuck, kudu, nyala and other antelopes.
There are a number of endemic fish species in the lakes and the Indian Ocean is a water wonderland with whales and dolphins, turtles and colourful tropical fish on the coral reefs
The Greater St Lucia area is renowned for its prolific birdlife including flamingoes, pelicans, herons, ducks, geese, storks and numerous resident and migrant birds.