Mar Menor, on the northern Mediterranean coast of Spain, is a coastal lagoon with a surface of 135 km2 , surrounded by agriculture fields and several towns, that support an important touristic activity. In addition, mining has been an historical activity on the region. In order to elucidate the input of metals supplied by Submarine Groundwater Discharge (SGD) to the lagoon and the spatial and temporal distribution of potentially toxic elements in this coastal ecosystem, the concentrations of dissolved metals (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As and Cd) were measured in surficial water courses (“ramblas”), groundwaters (including piezometers and boreholes) and lagoon waters. Samples were collected in two sampling campaigns (July and November, 2021), representing contrasting climatic seasons. These results were combined with the estimation of SGD fluxes to the coastal lagoon, allowing evaluating the fluxes of the studied pollutants. Occurrence of these pollutants in water from the lagoon has been previously registered, but none of those works has studied at the same time, and under a holistic point of view, all the possible aquatic pathways of dissolved metals, including the role of SGD as a conveyor of these potentially toxic elements.