Mangroves are a vital coastal system, offering habitat for economically important species such as fish, prawns and crabs, as well as mitigating coastal erosion. Port Pirie (Upper Spencer Gulf, South Australia) hosts one of the world’s largest Lead (Pb)–Zinc (Zn) smelters, in operation since 1889, and is well known for high levels of Pb, Zn, cadmium (Cd), copper (Cu) and arsenic (As) contamination on land and in the surrounding sub-tidal areas of Germein Bay. Extensive areas of mangroves (Avicennia marina) occur up to the smelter boundary, but metal(loid) contamination level and its impact on the plants themselves are unclear. This study assessed the scale of the contamination in which mangroves are living across Germein Bay. Total metal(loid) concentrations in sediments and plant tissues (pneumatophores, leaves) were measured via ICP-MS/OES after acid digestion at nine sites, along with sediment characteristics such as grain size and organic content. At four sites, chlorophyll in leaves was measured using a handheld meter, as a proxy of mangrove health. In situ marine diffusive gradients in thin films (DGT) was deployed in sediments. Mangroves were found living across large (correlated) gradients in concentration of Pb (9.81-14,488 mg/kg), Zn (10.7-62,097 mg/kg), As (2.34-614 mg/kg), Cd (0.06-160 mg/kg), Cu (1.34-788 mg/kg), but with no differences in chlorophyll apparent among highly and less contaminated sites. Bioaccumulation in A. marina pneumatophores and leaves correlated with total sediment concentrations, but was consistently lower than sediments for non-essential metal(loid)s (Pb: 0.22-319 mg/kg, As: 0.09-11.0 mg/kg, Cd: 0.04-2.20 mg/kg), and also lower for essential metals at high sediment concentrations (Zn: 15.9-1033 mg/kg, Cu: 1.33-38.8 mg/kg). This study highlights the resilience of A. marina in tolerating the highly contaminated sediments near the smelter at Port Pirie, presumably by minimizing (excluding) non-essential metal(loid) uptake and regulating the uptake of essential metals when in excess.