South Uist Machair and Lochs is a complex site along the west coast of South Uist in the Outer Hebrides off the north-west coast of Scotland. This area is of outstanding importance for its transition of habitats from acidic moorland to the calcareous coastal plain, and for the transition from freshwater to saltwater habitats. This complex includes outstanding examples of relict woodland, moorland and blanket bog, large oligotrophic lochs, acidic blacklands, wet and dry machair with eutrophic machair lochs, freshwater marsh, saltmarsh, coastal dunes and sandy and rocky shores. These areas are of outstanding importance for their populations of breeding waterbirds, especially Corncrake Crex crex, terns and waders. The densities of breeding waders are some of the highest in the world. The site is also important in winter in supporting large numbers of Sanderling Calidris alba on the coast.
The site also includes the subsumed SPA of Loch Druidibeg, Loch a' Machair and Loch Stilligary, a site that was subject to separate classification.