Laguna Verde Bay, a World Biosphere Reserve, seems to be barely uncontaminated due to its isolated geographical position (18 km south of Valparaíso, Chile) and low amount of anthropogenic activities. At its coastal border, there is a thermoelectric generator (using coal since 1939 and diesel since 2007 as fuel), a small village (≈10.000 inhabitants) and a local fishermen’s wharf. A freshwater creek flows into the beach, creating a small coastal pond that sporadically overflows into the bay. With the objective of estimating the origin of the Laguna Verde Bay surface sediments and its heavy metal pollution level, the content of Total Organic Matter (TOM), organic carbon to total nitrogen ratio (C:N ratio), stable carbon isotope ratio (δ13C), Al, Fe, Cu, Mn, Pb and Hg in samples collected in August 2015, were measured. According to the δ13C values, the sediment origin was mostly terrestrial, with an allochthonous content greater than 50%. Since there is no legislation in Chile to establish the heavy metal concentrations for unpolluted marine sediments, a normalized metal enrichment factor (NEF) was computed to infer the contamination level. Despite the high Fe and Pb contents in the bay’s sediment at two stations (13.3 mg g-1 and 18.0 µg g-1, respectively), the NEF values in the bay generally correspond to a low level of pollution.