The St Lucia Estuary is part of the iSimangaliso Wetland Park, which is a UNESCO World Heritage Site. It is characterised by instability and experiences ongoing anthropomorphic change, both of which have a significant impact on the biodiversity of the estuary and surrounding area. Brachyurans (true crabs) play an integral role in the functioning and maintenance of this ecosystem. They are a food source for organisms at higher trophic levels, maintain nutrient balance, regulate trophic flow and aerate dense mud through the construction of burrows. However, since the early survey of Millard and Broekhuysen (1970), no study has focussed on this taxon, the identification of which is confounded by the existence of cryptic and pseudocryptic species. This study provides a census of the brachyuran species inhabiting the St Lucia estuarine lake, highlighting the changes in diversity that have occurred in this region between 1948 and 2012. A total of thirty species were found in the area during this period, five of which have not been recorded in previous literature. The extent to which regional endemic species, such as Paratylodiplax blephariskios, have been affected by the dynamics of the system is discussed. The distribution and abundance of three key species, namely P. blephariskios, Neosarmatium africanum and Hymenosomaprojectum, are outlined; and possible reasons for observed changes are discussed. Future scenarios regarding the state of the estuary mouth and the stability of physico-chemical variables are also considered. Lastly, an annotated checklist illustrated by photographs is included to aid in identification of species for research and management purposes. KEY WORDS: Crustacea, Brachyura, South Africa, iSimangaliso Wetland Park, St Lucia estuarine system, true crabs, diversity, estuarine variability, illustrated checklist.